Answer:
To find the probability of picking two boys, we need to first know how many different ways she can pick the 7th and 8th grader.
There are 12 7th-graders and 8 8th-graders. So the total number of ways she can pick is:
12
×
8
=
96
To get two boys picked, there are 5 boys in the 7th-grade class and 4 in the 8th-grade class, so there are:
5
×
4
=
20
ways
Which gives us the probability of:
20
96
=
5
24
≅
21
%
Step-by-step explanation: