jmc

Question

In a history class, the probability of earning an A is .7 times the probability of earning a B, and the probability of earning a C is 1.4 times the probability of earning a B. Assuming that all grades are A, B, or C, how many B's will there be in a history class of 31 students?

Accepted Answer

Let x be the number of students who earn a B. Then we know that the number of students who get an A is .7x and the number of students who earn a C is 1.4x. Since every student in the class gets an A, B, or C and there are 31 students, this gives us the equation .7x + x + 1.4x = 31 3.1x = 31 x =10.