The remainder, when $$7^{103}$$ is divided by 23 , is equal to :
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We can use the Fermat’s Little Theorem i.e. $$a^{p-1} \equiv 1 \pmod{p}$$
Here, $$a = 7$$ and $$p = 23$$. Since 23 is prime and 7 is not a multiple of 23, we can apply the theorem:
$$7^{22} \equiv 1 \pmod{23}$$
Now, we have to break down 103 as a multiple of 22.
$$103 = (22 \times 4) + 15$$
$$\therefore\ $$ $$7^{103}=7^{22\times4+15}=\left(7^{22}\right)^{^4}\times7^{15}$$
We know that $$7^{22} \equiv 1 \pmod{23}$$.
$$7^{103} \equiv 1^4 \cdot 7^{15} \equiv 7^{15} \pmod{23}$$
Now, we need to calculate: $$7^{15}$$ mod 23
We know $$7^2=49\ ≡\ 3$$ (mod 23)
Similarly, $$7^4=49\ =3^2≡9$$(mod 23)
$$7^8=49\ =9^2=81≡12$$(mod 23)
Now, $$7^{15}=7^8\times7^4\times7^2\times7$$
Substituting the values: $$12\times9\times3\times7$$
$$12\times9=108≡16$$ (mod23)
$$16\times3=48≡2$$ (mod23)
$$2\times7=14$$ (mod23)
Hence, the final answer is 14.
$$25^{190} - 19^{190} - 8^{190} + 2^{190}$$ is divisible by
We need to determine whether $$25^{190} - 19^{190} - 8^{190} + 2^{190}$$ is divisible by 14, 34, both, or neither.
Note that $$14 = 2 \times 7$$ and $$34 = 2 \times 17$$. So we need to check divisibility by 2, 7, and 17.
To begin,
$$25^{190}$$ is odd, $$19^{190}$$ is odd, $$8^{190}$$ is even, $$2^{190}$$ is even.
So $$25^{190} - 19^{190} - 8^{190} + 2^{190} = (\text{odd} - \text{odd}) - (\text{even} - \text{even}) = \text{even} - \text{even} = \text{even}$$.
The expression is divisible by 2.
Next,
Regroup: $$(25^{190} - 8^{190}) - (19^{190} - 2^{190})$$.
Since $$25 - 8 = 17$$, by the algebraic identity $$a^n - b^n$$ is divisible by $$(a - b)$$, we get $$17 \mid (25^{190} - 8^{190})$$.
Since $$19 - 2 = 17$$, similarly $$17 \mid (19^{190} - 2^{190})$$.
Therefore $$17 \mid \left[(25^{190} - 8^{190}) - (19^{190} - 2^{190})\right]$$.
From this,
Since the expression is divisible by both 2 and 17, and $$\gcd(2, 17) = 1$$, the expression is divisible by $$2 \times 17 = 34$$.
Continuing,
We check modulo 7:
$$25 \equiv 4 \pmod{7}$$, $$19 \equiv 5 \pmod{7}$$, $$8 \equiv 1 \pmod{7}$$, $$2 \equiv 2 \pmod{7}$$.
By Fermat's little theorem, $$a^6 \equiv 1 \pmod{7}$$ for $$\gcd(a, 7) = 1$$.
Since $$190 = 6 \times 31 + 4$$, we have $$a^{190} \equiv a^4 \pmod{7}$$.
$$4^4 = 256 \equiv 4 \pmod{7}$$
$$5^4 = 625 \equiv 2 \pmod{7}$$
$$1^4 = 1 \pmod{7}$$
$$2^4 = 16 \equiv 2 \pmod{7}$$
So the expression $$\equiv 4 - 2 - 1 + 2 = 3 \pmod{7}$$.
Since $$3 \not\equiv 0 \pmod{7}$$, the expression is not divisible by 7, and hence not divisible by 14.
Conclusion: The expression is divisible by 34 but not by 14.
The correct answer is Option C.
The remainder when $$(2023)^{2023}$$ is divided by 35 is
We need to find the remainder when $$(2023)^{2023}$$ is divided by $$35$$.
Since $$35 = 5 \times 7$$ and $$\gcd(5, 7) = 1$$, we use the Chinese Remainder Theorem.
Find $$(2023)^{2023} \pmod{5}$$.
$$2023 = 404 \times 5 + 3$$, so $$2023 \equiv 3 \pmod{5}$$.
By Fermat's Little Theorem, $$3^4 \equiv 1 \pmod{5}$$.
$$2023 = 4 \times 505 + 3$$, so $$2023 \equiv 3 \pmod{4}$$.
Therefore: $$3^{2023} \equiv 3^3 = 27 \equiv 2 \pmod{5}$$.
Find $$(2023)^{2023} \pmod{7}$$.
$$2023 = 289 \times 7$$, so $$2023 \equiv 0 \pmod{7}$$.
Therefore: $$(2023)^{2023} \equiv 0 \pmod{7}$$.
Apply the Chinese Remainder Theorem.
We need $$x$$ such that:
$$x \equiv 2 \pmod{5}$$ and $$x \equiv 0 \pmod{7}$$.
From the second condition, $$x = 7k$$ for some integer $$k$$.
Substituting: $$7k \equiv 2 \pmod{5} \implies 2k \equiv 2 \pmod{5} \implies k \equiv 1 \pmod{5}$$.
So $$k = 5m + 1$$ and $$x = 7(5m + 1) = 35m + 7$$.
The remainder when $$(2023)^{2023}$$ is divided by $$35$$ is $$\boxed{7}$$.
The number of elements in the set $$\{n \in \mathbb{N} : 10 \leq n \leq 100$$ and $$3^n - 3$$ is a multiple of $$7\}$$ is _____.
We need $$3^n - 3 \equiv 0 \pmod{7}$$, i.e., $$3^n \equiv 3 \pmod{7}$$, i.e., $$3^{n-1} \equiv 1 \pmod{7}$$.
The order of 3 modulo 7: $$3^1 = 3$$, $$3^2 = 9 \equiv 2$$, $$3^3 = 27 \equiv 6$$, $$3^4 = 81 \equiv 4$$, $$3^5 = 243 \equiv 5$$, $$3^6 = 729 \equiv 1 \pmod{7}$$.
So $$3^{n-1} \equiv 1 \pmod{7}$$ when $$6 | (n-1)$$, i.e., $$n \equiv 1 \pmod{6}$$.
Values of $$n$$ in $$[10, 100]$$ with $$n \equiv 1 \pmod{6}$$:
$$n = 13$$, $$19$$, $$25$$, $$31$$, $$37$$, $$43$$, $$49$$, $$55$$, $$61$$, $$67$$, $$73$$, $$79$$, $$85$$, $$91$$, $$97$$
Count: $$\frac{97 - 13}{6} + 1 = \frac{84}{6} + 1 = 14 + 1 = 15$$
The answer is $$\mathbf{15}$$.
The remainder on dividing $$5^{99}$$ by 11 is ______.
We need to find $$5^{99} \mod 11$$.
By Fermat's Little Theorem, since 11 is prime and $$\gcd(5, 11) = 1$$:
$$ 5^{10} \equiv 1 \pmod{11} $$
Dividing the exponent: $$99 = 10 \times 9 + 9$$
$$ 5^{99} = (5^{10})^9 \times 5^9 \equiv 1^9 \times 5^9 = 5^9 \pmod{11} $$
Computing $$5^9 \mod 11$$ step by step:
$$5^1 \equiv 5$$
$$5^2 \equiv 25 \equiv 3 \pmod{11}$$
$$5^4 \equiv 3^2 = 9 \pmod{11}$$
$$5^8 \equiv 9^2 = 81 \equiv 4 \pmod{11}$$
$$5^9 = 5^8 \times 5 \equiv 4 \times 5 = 20 \equiv 9 \pmod{11}$$
The remainder is 9.
The remainder when $$(2021)^{2023}$$ is divided by $$7$$ is
We need to find the remainder when $$(2021)^{2023}$$ is divided by 7.
Find $$2021 \mod 7$$.
$$2021 = 288 \times 7 + 5$$
So $$2021 \equiv 5 \pmod{7}$$
Find the pattern of powers of 5 modulo 7.
$$5^1 \equiv 5 \pmod{7}$$
$$5^2 \equiv 25 \equiv 4 \pmod{7}$$
$$5^3 \equiv 20 \equiv 6 \pmod{7}$$
$$5^4 \equiv 30 \equiv 2 \pmod{7}$$
$$5^5 \equiv 10 \equiv 3 \pmod{7}$$
$$5^6 \equiv 15 \equiv 1 \pmod{7}$$
The powers of 5 repeat with a cycle of length 6 (by Fermat's Little Theorem).
Find $$2023 \mod 6$$.
$$2023 = 337 \times 6 + 1$$
So $$2023 \equiv 1 \pmod{6}$$
Compute the remainder.
$$(2021)^{2023} \equiv 5^{2023} \equiv 5^1 \equiv 5 \pmod{7}$$
The remainder is $$\textbf{5}$$.
The correct answer is Option D.
The remainder when $$(11)^{1011} + (1011)^{11}$$ is divided by $$9$$ is
We want to determine the remainder when $$(11)^{1011} + (1011)^{11}$$ is divided by 9. First, observe that $$11 \equiv 2 \pmod{9}$$ so that $$11^{1011} \equiv 2^{1011} \pmod{9}$$. To compute this, note that the powers of 2 modulo 9 cycle with period 6:
$$2^1 \equiv 2, \quad 2^2 \equiv 4, \quad 2^3 \equiv 8, \quad 2^4 \equiv 7, \quad 2^5 \equiv 5, \quad 2^6 \equiv 1 \pmod{9}$$
Since $$1011 = 6 \times 168 + 3$$, it follows that $$2^{1011} \equiv 2^3 \equiv 8 \pmod{9}$$.
Next, we reduce $$1011^{11}$$ modulo 9. Writing $$1011 = 112 \times 9 + 3$$ shows that $$1011 \equiv 3 \pmod{9}$$, hence $$1011^{11} \equiv 3^{11} \pmod{9}$$. Because $$3^2 = 9 \equiv 0 \pmod{9}$$, one factor of $$3^2$$ makes the product a multiple of 9, so $$3^{11} = 3^2 \times 3^9 = 9 \times 3^9 \equiv 0 \pmod{9}$$.
Adding these results gives
$$11^{1011} + 1011^{11} \equiv 8 + 0 \equiv 8 \pmod{9}$$
The correct answer is Option B: $$8$$.
The remainder when $$3^{2022}$$ is divided by $$5$$ is
$$3^{2022} = (3^2)^{1011}$$
$$(3^2)^{1011} \equiv (-1)^{1011} \pmod{5}$$
$$(-1)^{1011} = -1$$
Now we know that a remainder of $$-1$$ is not the standard way. So to convert a negative remainder back to a positive one, we can just add the divisor ($$5$$):
Hence, $$3^{2022} \equiv 4 \pmod{5}$$
Alternative Method 1:
Using Fermat's Little Theorem: $$a^{p-1} \equiv 1 \pmod{p}$$
So, we can say, $$3^{5-1} \equiv 3^4 \equiv 1 \pmod{5}$$
Now, $$2022 = 4 \times 505 + 2$$
Hence, we can say, $$3^{2022} = 3^{4 \times 505 + 2} = (3^4)^{505} \times 3^2$$
$$3^{2022} \equiv (1)^{505} \times 3^2 \pmod{5}$$
$$3^{2022} \equiv 1 \times 9 \pmod{5}$$
$$3^{2022} \equiv 4 \pmod{5}$$
Alternative Method 2:
We can also find the pattern.
$$3^1 \equiv 3 \pmod{5}$$
$$3^2 = 9 \equiv 4 \pmod{5}$$
$$3^3 = 27 \equiv 2 \pmod{5}$$
$$3^4 = 81 \equiv 1 \pmod{5}$$
$$3^5 = 243 \equiv 3 \pmod{5}$$
So the cycle repeats: 3, 4, 2, 1
Exponent is 2022.
Hence, $$2022 \div 4 = 505 \text{ with a remainder of } 2$$
Since the remainder is $$2$$, the result would be same as the second position in our cycle ($$3^2 \equiv 4 \pmod{5}$$).
A natural number has prime factorization given by $$n = 2^x 3^y 5^z$$, where $$y$$ and $$z$$ are such that $$y + z = 5$$ and $$y^{-1} + z^{-1} = \frac{5}{6}$$, $$y > z$$. Then the number of odd divisors of $$n$$, including 1, is:
We are given $$n = 2^x 3^y 5^z$$ where $$y + z = 5$$ and $$y^{-1} + z^{-1} = \dfrac{5}{6}$$, with $$y > z$$.
From the second equation, $$\dfrac{1}{y} + \dfrac{1}{z} = \dfrac{y + z}{yz} = \dfrac{5}{yz} = \dfrac{5}{6}$$, which gives $$yz = 6$$.
So $$y$$ and $$z$$ are roots of $$t^2 - 5t + 6 = 0$$, i.e., $$(t - 3)(t - 2) = 0$$. Since $$y > z$$, we get $$y = 3$$ and $$z = 2$$.
Thus $$n = 2^x \cdot 3^3 \cdot 5^2$$. The odd divisors of $$n$$ are the divisors of $$3^3 \cdot 5^2$$ (we exclude all factors of 2). The number of such divisors is $$(3 + 1)(2 + 1) = 12$$.
The answer is $$12$$.
If $$(2021)^{3762}$$ is divided by 17, then the remainder is ________.
We need the remainder when $$(2021)^{3762}$$ is divided by 17.
First, $$2021 \mod 17$$: since $$17 \times 118 = 2006$$, we get $$2021 - 2006 = 15$$, so $$2021 \equiv 15 \equiv -2 \pmod{17}$$.
Since the exponent 3762 is even, $$(2021)^{3762} \equiv (-2)^{3762} = 2^{3762} \pmod{17}$$.
By Fermat's Little Theorem (17 is prime, $$\gcd(2,17)=1$$): $$2^{16} \equiv 1 \pmod{17}$$.
Dividing: $$3762 = 16 \times 235 + 2$$, so $$2^{3762} = (2^{16})^{235} \cdot 2^2 \equiv 1 \cdot 4 = 4 \pmod{17}$$.
The remainder is 4.
The sum of all natural numbers $$n$$ such that $$100 < n < 200$$ and H.C.F. $$(91, n) > 1$$ is:
We are asked to consider all natural numbers $$n$$ that satisfy the double inequality $$100<n<200$$ and whose highest common factor with $$91$$ is greater than $$1$$.
First, we factorise $$91$$ so that we know which prime numbers can possibly divide both $$91$$ and $$n$$.
We have $$91 = 7 \times 13$$, and $$7$$ and $$13$$ are primes.
If the H.C.F. (also called G.C.D.) of $$91$$ and $$n$$ is to be greater than $$1$$, then $$n$$ must share at least one of the prime factors $$7$$ or $$13$$ with $$91$$. Equivalently, $$n$$ must be divisible by $$7$$ or by $$13$$ (or by both).
So we now list every multiple of $$7$$ and every multiple of $$13$$ that lies strictly between $$100$$ and $$200$$.
Multiples of $$7$$ in the required interval
We solve $$7k$$ with $$100<7k<200$$.
Dividing by $$7$$ gives $$\dfrac{100}{7}<k<\dfrac{200}{7}$$, i.e. $$14.28\dots<k<28.57\dots$$. Hence the integer values of $$k$$ are $$k=15,16,\dots ,28$$. Writing the corresponding numbers:
$$\begin{aligned} 7\times15 &= 105 \\ 7\times16 &= 112 \\ 7\times17 &= 119 \\ 7\times18 &= 126 \\ 7\times19 &= 133 \\ 7\times20 &= 140 \\ 7\times21 &= 147 \\ 7\times22 &= 154 \\ 7\times23 &= 161 \\ 7\times24 &= 168 \\ 7\times25 &= 175 \\ 7\times26 &= 182 \\ 7\times27 &= 189 \\ 7\times28 &= 196 \end{aligned}$$
So the complete list of admissible multiples of $$7$$ is
$$105,112,119,126,133,140,147,154,161,168,175,182,189,196.$$
Multiples of $$13$$ in the required interval
We solve $$13m$$ with $$100<13m<200$$.
Dividing by $$13$$ gives $$\dfrac{100}{13}<m<\dfrac{200}{13}$$, i.e. $$7.69\dots<m<15.38\dots$$. Hence the integer values of $$m$$ are $$m=8,9,\dots ,15$$. Writing the corresponding numbers:
$$\begin{aligned} 13\times8 &= 104 \\ 13\times9 &= 117 \\ 13\times10 &= 130 \\ 13\times11 &= 143 \\ 13\times12 &= 156 \\ 13\times13 &= 169 \\ 13\times14 &= 182 \\ 13\times15 &= 195 \end{aligned}$$
So the complete list of admissible multiples of $$13$$ is
$$104,117,130,143,156,169,182,195.$$
Combining the two lists
Every number in either list satisfies the H.C.F. condition, but we must beware of double counting any number that is simultaneously a multiple of $$7$$ and $$13$$.
Notice that $$182$$ appears in both lists because $$182 = 7\times26 = 13\times14$$ (since $$182$$ is itself $$91\times2$$). No other number is common to the two lists.
Sum of all admissible numbers
First sum all the multiples of $$7$$ we found:
$$\begin{aligned} &105+112+119+126+133+140+147+154+161+168+175+182+189+196 \\ &= (105+112) + (119+126) + (133+140) + (147+154) + (161+168) + (175+182) + (189+196) \\ &= 217 + 245 + 273 + 301 + 329 + 357 + 385 \\ &= 2107 \end{aligned}$$
Next sum all the multiples of $$13$$ we found:
$$\begin{aligned} &104+117+130+143+156+169+182+195 \\ &= (104+117) + (130+143) + (156+169) + (182+195) \\ &= 221 + 273 + 325 + 377 \\ &= 1196 \end{aligned}$$
Because $$182$$ lies in both lists, it has been counted twice, once in each subtotal. To obtain the correct total we subtract this overlap once.
Therefore the required sum is
$$2107 + 1196 - 182 = 3121.$$
Hence, the correct answer is Option C.
If the fractional part of the number $$\frac{2^{403}}{15}$$ is $$\frac{k}{15}$$, then $$k$$ is equal to:
We want the fractional part of $$\dfrac{2^{403}}{15}$$. By definition, if we divide $$2^{403}$$ by $$15$$ we can write
$$2^{403}=15q+k$$
where $$q$$ is the quotient and $$k$$ is the remainder satisfying $$0\le k<15$$. Then
$$\dfrac{2^{403}}{15}=q+\dfrac{k}{15},$$
so the fractional part is exactly $$\dfrac{k}{15}$$. Our task is therefore to find the remainder $$k$$ when $$2^{403}$$ is divided by $$15$$; symbolically, we must evaluate
$$k\equiv 2^{403}\pmod{15}.$$
To do this efficiently we recall Euler’s theorem. First we note that $$\gcd(2,15)=1$$, so Euler’s theorem applies. The theorem states:
$$\text{If }\gcd(a,n)=1,\text{ then }a^{\phi(n)}\equiv1\pmod n.$$
Here $$n=15$$, so we compute Euler’s totient function $$\phi(15)$$. Since $$15=3\cdot5$$ with both factors prime, we have
$$\phi(15)=15\left(1-\dfrac13\right)\left(1-\dfrac15\right)=15\cdot\dfrac23\cdot\dfrac45=8.$$
Therefore, by Euler’s theorem,
$$2^{8}\equiv1\pmod{15}.$$
Now we use this congruence to break the large exponent $$403$$ into manageable parts. Write the exponent in the form
$$403=8\cdot50+3.$$
So,
$$2^{403}=2^{8\cdot50+3}=2^{8\cdot50}\cdot2^{3}=\left(2^{8}\right)^{50}\cdot2^{3}.$$
Since $$2^{8}\equiv1\pmod{15},$$ raising it to any power keeps it congruent to $$1$$:
$$\left(2^{8}\right)^{50}\equiv1^{50}\equiv1\pmod{15}.$$
Hence,
$$2^{403}\equiv1\cdot2^{3}\pmod{15}.$$
We still need $$2^{3}$$, and that is straightforward:
$$2^{3}=8.$$
So we finally have
$$2^{403}\equiv8\pmod{15}.$$
Comparing this with our earlier definition $$2^{403}=15q+k,$$ we see the remainder is
$$k=8.$$
Because $$0\le k<15,$$ this value is valid. The fractional part of $$\dfrac{2^{403}}{15}$$ is therefore $$\dfrac{8}{15},$$ and the asked integer is $$k=8$$.
Hence, the correct answer is Option C.
For integers $$m$$ and $$n$$, both greater than 1, consider the following three statements : P : m divides n Q : m divides $$n^2$$ R : m is prime, then
We are given three statements for integers $$m$$ and $$n$$, both greater than 1:
- P: $$m$$ divides $$n$$ (i.e., $$n$$ is divisible by $$m$$, written as $$m \mid n$$)
- Q: $$m$$ divides $$n^2$$ (i.e., $$m \mid n^2$$)
- R: $$m$$ is prime
We need to evaluate the logical implications given in the options and determine which one is always true.
Starting with Option A: $$Q \wedge R \rightarrow P$$. This means if Q and R are both true, then P must be true. That is, if $$m$$ divides $$n^2$$ and $$m$$ is prime, then $$m$$ divides $$n$$.
Assume Q and R are true: $$m \mid n^2$$ and $$m$$ is prime. Since $$m$$ is prime and divides $$n^2$$, and $$n^2 = n \times n$$, by Euclid's lemma (which states that if a prime divides a product, it must divide at least one factor), $$m$$ must divide $$n$$. Therefore, P is true. This implication holds.
Now, Option B: $$P \wedge Q \rightarrow R$$. This means if P and Q are true, then R must be true. That is, if $$m$$ divides $$n$$ and $$m$$ divides $$n^2$$, then $$m$$ is prime.
Note that if P is true ($$m \mid n$$), then Q ($$m \mid n^2$$) is automatically true because if $$n = m \cdot k$$ for some integer $$k$$, then $$n^2 = m \cdot (m \cdot k^2)$$, so $$m \mid n^2$$. Thus, the premise $$P \wedge Q$$ reduces to P being true. But the conclusion requires $$m$$ to be prime, which may not hold. For example, let $$m = 4$$ (composite) and $$n = 4$$. Then P: $$4 \mid 4$$ is true (since $$4 = 4 \times 1$$), and Q: $$4 \mid 16$$ is true (since $$16 = 4 \times 4$$), but R: $$m = 4$$ is not prime. Since the premise is true and the conclusion is false, this implication is not always true.
Option C: $$Q \rightarrow R$$. This means if Q is true, then R must be true. That is, if $$m$$ divides $$n^2$$, then $$m$$ is prime.
This is not always true. For example, let $$m = 4$$ and $$n = 2$$. Then Q: $$4 \mid 2^2 = 4$$ is true (since $$4 = 4 \times 1$$), but R: $$m = 4$$ is not prime. Thus, this implication is false.
Option D: $$Q \rightarrow P$$. This means if Q is true, then P must be true. That is, if $$m$$ divides $$n^2$$, then $$m$$ divides $$n$$.
This is not always true. For example, let $$m = 4$$ and $$n = 2$$. Then Q: $$4 \mid 2^2 = 4$$ is true, but P: $$4 \mid 2$$ is false (since $$2 \div 4 = 0.5$$, not an integer). Another example: $$m = 9$$ and $$n = 3$$. Then Q: $$9 \mid 3^2 = 9$$ is true (since $$9 = 9 \times 1$$), but P: $$9 \mid 3$$ is false. Hence, this implication is false.
Only Option A is always true. Therefore, the correct answer is Option A.
Hence, the correct answer is Option A.
The remainder when $$428^{2024}$$ is divided by 21 is __________
Firstly, we need to find the remainder when 428 is divided by 21.
$$428 = (21 \times 20) + 8$$
So, $$428 \equiv 8 \pmod{21}$$.
Hence, we can say: $$428^{2024} \equiv 8^{2024} \pmod{21}$$
Now, we can find the remainders for the first few powers of 8 so as to find any recurring pattern of the remainders.
$$8^1\ ≡\ 8$$ (mod 21)
$$8^2=24$$ (mod 21)
Now, find the remainder of 64 divided by 21: $$64 = (21 \times 3) + 1$$
So, $$8^2 \equiv 1 \pmod{21}$$.
Now, because $$8^2 \equiv 1 \pmod{21}$$, we can express the large exponent, 2024, in terms of 2. We divide 2024 by 2:
$$2024 = 2 \times 1012$$
So, we can say, $$8^{2024}=\left(8^2\right)^{2024}$$
Substitute 1 for $$8^2$$,
$$(8^2)^{1012} \equiv 1^{1012} \pmod{21}$$
Hence, the remainder wil be 1.
$$50^{th}$$ root of a number $$x$$ is $$12$$ and $$50^{th}$$ root of another number $$y$$ is $$18$$. Then the remainder obtained on dividing $$(x + y)$$ by $$25$$ is ______.
We are given that the $$50^{th}$$ root of $$x$$ is $$12$$ and the $$50^{th}$$ root of $$y$$ is $$18$$.
So $$x = 12^{50}$$ and $$y = 18^{50}$$.
By Euler's theorem, since $$\gcd(12, 25) = 1$$ and $$\phi(25) = 20$$, we have $$12^{20} \equiv 1 \pmod{25}$$.
$$12^{50} = 12^{20 \cdot 2} \cdot 12^{10} = (12^{20})^2 \cdot 12^{10} \equiv 12^{10} \pmod{25}$$
Now compute $$12^{10} \pmod{25}$$:
$$12^2 = 144 \equiv 19 \pmod{25}$$
$$12^4 = 19^2 = 361 \equiv 11 \pmod{25}$$
$$12^8 = 11^2 = 121 \equiv 21 \pmod{25}$$
$$12^{10} = 12^8 \cdot 12^2 = 21 \times 19 = 399 \equiv 24 \pmod{25}$$
$$18^2 = 324 \equiv 24 \equiv -1 \pmod{25}$$
$$18^{50} = (18^2)^{25} = (-1)^{25} = -1 \equiv 24 \pmod{25}$$
$$(x + y) \pmod{25} = (24 + 24) \pmod{25} = 48 \pmod{25} = 23$$
The remainder is $$\boxed{23}$$.
Let the number $$(22)^{2022} + (2022)^{22}$$ leave the remainder $$\alpha$$ when divided by 3 and $$\beta$$ when divided by 7. Then $$(\alpha^2 + \beta^2)$$ is equal to
$$22^{2022} + 2022^{22} \pmod{3}$$:
$$22 \equiv 1 \pmod{3}$$, so $$22^{2022} \equiv 1$$. $$2022 \equiv 0 \pmod{3}$$, so $$2022^{22} \equiv 0$$.
$$\alpha = 1 + 0 = 1$$.
$$22^{2022} + 2022^{22} \pmod{7}$$:
$$22 \equiv 1 \pmod{7}$$, so $$22^{2022} \equiv 1$$. $$2022 = 288 \times 7 + 6$$, so $$2022 \equiv -1 \pmod{7}$$, $$2022^{22} \equiv 1$$.
$$\beta = 1 + 1 = 2$$.
$$\alpha^2 + \beta^2 = 1 + 4 = 5$$.
The correct answer is Option 3: 5.
The product of the last two digits of $$(1919)^{1919}$$ is _____.
To obtain the product of the last two digits of $$(1919)^{1919}$$ we must first find those two digits, i.e. evaluate $$(1919)^{1919} \pmod{100}$$.
Step 1 : Reduce the base modulo 100
$$1919 \equiv 19 \pmod{100}$$
Hence $$ (1919)^{1919} \equiv 19^{1919} \pmod{100} $$.
Step 2 : Reduce the exponent using Euler’s theorem
Since $$\gcd(19,100)=1$$, Euler’s theorem gives $$19^{\phi(100)} \equiv 1 \pmod{100}$$.
Factorising $$100 = 2^{2}\cdot5^{2}$$,
$$\phi(100)=100\left(1-\frac{1}{2}\right)\left(1-\frac{1}{5}\right)=40$$.
Therefore the powers of 19 repeat every 40:
$$19^{40} \equiv 1 \pmod{100}$$.
Now reduce the exponent 1919 modulo 40:
$$1919 = 40\times47 + 39 \quad\Longrightarrow\quad 1919 \equiv 39 \pmod{40}$$.
Thus
$$19^{1919} \equiv 19^{39} \pmod{100} \quad -(1)$$
Step 3 : Shorten the exponent further (optional but quicker)
We shall show that $$19^{10} \equiv 1 \pmod{100}$$, which will cut the power down even more.
Compute successive powers of 19 (always keeping only the last two digits):
$$19^{1}=19$$
$$19^{2}=361\equiv61$$
$$19^{3}=61\cdot19=1159\equiv59$$
$$19^{4}=59\cdot19=1121\equiv21$$
$$19^{5}=21\cdot19=399\equiv99$$
$$19^{6}=99\cdot19=1881\equiv81$$
$$19^{7}=81\cdot19=1539\equiv39$$
$$19^{8}=39\cdot19=741\equiv41$$
$$19^{9}=41\cdot19=779\equiv79$$
$$19^{10}=79\cdot19=1501\equiv01\equiv1$$
Since $$19^{10}\equiv1\pmod{100}$$, rewrite the required power:
$$19^{39}=19^{10\cdot3}\cdot19^{9}\equiv(19^{10})^{3}\cdot19^{9}\equiv1^{3}\cdot19^{9}\equiv19^{9}\pmod{100}$$.
Step 4 : Evaluate $$19^{9}\pmod{100}$$ (already calculated above)
From the list, $$19^{9}\equiv79\pmod{100}$$.
Hence the last two digits of $$(1919)^{1919}$$ are 7 and 9.
Step 5 : Required product
Product of the digits $$7 \times 9 = 63$$.
Final Answer : 63
Remainder when $$64^{32^{32}}$$ is divided by $$9$$ is equal to ______.
To find: the remainder of $$64^{32^{32}}$$
We know $$9\times\ 7=63$$
$$\therefore$$ When we divide $$\frac{64}{7}$$ we get remainder 1.
So we can also write $$64^{32^{32}}$$ as $$1^{32^{32}}$$
When we divide $$1^{32^{32}}$$ by 9 we get a remainder 1.
$$\therefore$$ correct answer is 1.
ALTERNATE METHOD:
Simplify 64 mod 9
$$64=\left(9\times\ 7\right)+1$$
So, 64 ≡1 (mod 9)
Now raise both side to the power $$32^{32}$$
$$\therefore$$ $$64^{32^{32}}≡1^{32^{32}}$$ (mod 9)
Since any power of 1 is 1
$$\therefore$$ $$64^{32^{32}}$$ is divided by 9 the remainder is 1.