Question

In a class, 40% of the students attended regularly, 60% did not. Of the 40% who did, 70% of them got a B or higher. Of the 60% who did not, 35% got a B or higher. What is the probability that a randomly chosen student will have scored a B or higher?

Answer 1

you need to do the venn diagram!

Answer 2

P(≥B) = 0.4(0.7) + 0.6(0.35) = 0.364
The 1st case is when the student gets ≥B when he attends school regularly
The 2nd case is when the student gets ≥B when he does not attend school regularly
Since both are mutually exclusive, you add them.