The answer given in the book is $1/4$ but i don't understand how that can be so. What i understand from the question is this based on conditional probability. i have to find :
P(one number being $2$ , GIVEN sum of two numbers is odd) = P(2 $\cap$ odd sum)$\div$ P(odd sum)
but i'm not sure how to do/calculate this. Any help? Also , do correct me if my understanding is wrong.
edit : Repeats are not allowed in selection. Forgot to add this.
Best Answer
Since the sum is odd, one number is odd and the other is even. Thus there are $2\times 5\times 4 = 40$ choices for selecting a pair of number whose sum is odd. Of these pairs, there are $2\times 5 = 10$ pairs with one of the numbers is $2$. Thus the answer is $\dfrac{10}{40} = \dfrac{1}{4}$.