Question

Mr. Thompson has been grading tests and has not had any A's. Assume the probability of making an A on her test is .15 and the tests are independent (no cheating), then how many tests should she expect to grade until she grades one that is an A?

Answer 1

To find the expected number of tests Mr. Thompson should grade until he grades one that is an A, we can use the concept of the geometric distribution. The expected number of tests until he grades an A is 6.67.

Step-by-step explanation:

To find the expected number of tests Mr. Thompson should grade until he grades one that is an A, we can use the concept of the geometric distribution.

The probability of making an A on a test is 0.15, which means the probability of not making an A is 0.85.

The expected value of a geometric distribution is given by E(X) = 1/p, where p is the probability of success.

For Mr. Thompson, the expected number of tests until he grades an A is 1/0.15 = 6.67 (rounded to 2 decimal places).