Hello. There are 3 boys, 3 pictures and 3 car names.

A task is just to connect car names into their pictures.

If a boy connects car names into pictures randomly, what is a probability function

on number Y of correct choises?

Let's see, 3 pictures, 3 cars and because it is enough that one boy connects, so

that would be: {1,2,3,4,5,6,7} and sum of that is 28.

( Unless, we have to deal correct choises: 3 pictures = 1/3. 3 car names = 1/3. ...)

Next step is division.

Thus, 1/28, 2/28, 3/28, 4/28, 5/28, 6/28, 7/28.

2/28 = 1/14, 4/28 = 1/7 and 7/28 = 1/4.

Hence, pdf ( probability density function ) on number Y of correct choises is

{1/28, 1/14, 3/28, 1/7, 5/28, 6/28, 1/4}