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The mean and variance for seven observations are 8 and 16 respectively. If 5 of the observations are 2, 4, 10, 12, 14, then the product of the remaining two observations is:
We are told that there are altogether seven observations whose arithmetic mean (average) is $$8$$ and whose variance is $$16$$. Five of these observations are already known: $$2,\,4,\,10,\,12,\,14$$. We must find the product of the two unknown observations; let us denote them by $$x$$ and $$y$$.
First, we recall the formula for the mean of $$n$$ observations:
$$\text{Mean}=\dfrac{\sum_{i=1}^{n}x_i}{n}.$$
Here the mean is $$8$$ and the number of observations is $$7$$, so
$$8=\dfrac{2+4+10+12+14+x+y}{7}.$$
Multiplying both sides by $$7$$ gives
$$56=2+4+10+12+14+x+y.$$
Adding the five known numbers on the right-hand side, we have
$$2+4+10+12+14=42,$$
so the equation becomes
$$56=42+x+y.$$
Subtracting $$42$$ from both sides, we get the sum of the two unknown observations:
$$x+y=14. \quad -(1)$$
Next, we use the formula for the variance of $$n$$ observations:
$$\sigma^{2}=\dfrac{\sum_{i=1}^{n}x_i^{2}}{n}-\left(\text{Mean}\right)^{2}.$$
The variance is given as $$16$$, so
$$16=\dfrac{2^{2}+4^{2}+10^{2}+12^{2}+14^{2}+x^{2}+y^{2}}{7}-8^{2}.$$
Because $$8^{2}=64$$, we rewrite the equation as
$$16=\dfrac{2^{2}+4^{2}+10^{2}+12^{2}+14^{2}+x^{2}+y^{2}}{7}-64.$$
Adding $$64$$ to both sides gives
$$16+64=\dfrac{2^{2}+4^{2}+10^{2}+12^{2}+14^{2}+x^{2}+y^{2}}{7},$$
so
$$80=\dfrac{2^{2}+4^{2}+10^{2}+12^{2}+14^{2}+x^{2}+y^{2}}{7}.$$
Multiplying by $$7$$ yields the total of all seven squares:
$$560=2^{2}+4^{2}+10^{2}+12^{2}+14^{2}+x^{2}+y^{2}. \quad -(2)$$
Now we compute the sum of squares of the five known observations:
$$2^{2}=4,\quad4^{2}=16,\quad10^{2}=100,\quad12^{2}=144,\quad14^{2}=196.$$ Adding these, we get
$$4+16+100+144+196=460.$$
Substituting this result into equation (2), we find the combined squares of the unknowns:
$$560=460+x^{2}+y^{2}\;\Longrightarrow\;x^{2}+y^{2}=560-460=100. \quad -(3)$$
We now possess two key relations: the sum $$x+y=14$$ from (1) and the sum of squares $$x^{2}+y^{2}=100$$ from (3). To obtain the product $$xy$$, we use the algebraic identity
$$(x+y)^{2}=x^{2}+y^{2}+2xy.$$
Substituting the known values, we have
$$14^{2}=100+2xy.$$
Since $$14^{2}=196$$, the equation becomes
$$196=100+2xy.$$
Subtracting $$100$$ from both sides gives
$$96=2xy,$$
and dividing by $$2$$ yields
$$xy=48.$$
Therefore, the product of the remaining two observations is $$48$$.
Hence, the correct answer is Option A.
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