Question

A science class has

3
girls and
7
boys in the seventh grade and
2
girls and
2
boys in the eighth grade. The teacher randomly selects a seventh grader and an eighth grader from the class for a competition. What is the probability that the students she selects are both boys?

Answer 1

the probability that the teacher selects both boys from a seventh grader and eighth grader.
first calculate the probility that it is boy in each grade
7th
x = 7 / ( 7 + 3) = 7 / 10

8th
y = 2 / (2 + 2) = 1 / 2

so the probability
P = ( 7 / 10 ) ( 1 / 2 )
P = 0.35