each of two boys, al and bob, and two girls, carol and dee, were given cards with a different integer from 1 to 4, inclusive, written on them.
What is the probability that the sum of the numbers on the cards given to the boys is even?
답 1/3
이거 저는 남자아이가 가진 두 카드의 합이 짝수일 확률이니까. 1/2 이라고 생각하는데 왜 1/3 일까요?