Question 64
Out of 20 consecutive positive integers, two are chosen at random. The probability that their sum is odd is ..........
Solution
Out of 20 consecutive positive integers, 10 are even numbers and 10 odd numbers.
Sum is odd when one number of even and other is odd.
Favourable cases = $$10_{C_{1}} * 10_{C_{1}}$$ = 10 * 10
Total cases = $$20_{C_{2}}$$ = 10 * 19
Required probability = $$\frac{10 * 10}{10 * 19} = \frac{10}{19}$$
