The probability that a student will pass an exam on any trial is 0.7. What is the expected number of trials needed to pass the exam?
A) 0.420
B) 0.428
C) 0.429
D) 1.420
E) 1.430

Question

Quizplus · Accepted Answer

The expected value of a geometric distribution (number of trials until success) with probability p is 1/p.
Therefore, in this case, the expected number of trials until passing the exam is 1/0.7 = 1.429, which is closest to option C (0.429) after rounding to three decimal places.

The Probability That a Student Will Pass an Exam on Any