Two numbers are selected at random from integers 1 through 9. If the sum is even, find the probability that both the numbers are odd.

Explanation

Sum will be even if both the selected numbers are even or both the numbers are odd.

Let `A = `Event that sum of two numbers is even.

Here, we can select two numbers from `5` odd numbers or from `4` even numbers.

`:. n(A) = C(5,2)+C(4,2) = 10+6 = 16.`

Let `B = `Event that both numbers are odd.

`:. n(B) = C(5,2) = 10`



...