Find the expected value of the number of tests taken.
A calculus instructor uses computer aided instruction and allows students to take the midterm exam as many times as essential until a passing grade is obtained. Following is a record of the number of students in a class of 20 who took the test each number of times.
|
Students
|
Number of tests
|
|
10
|
1
|
|
7
|
2
|
|
2
|
3
|
|
1
|
4
|
Find out the expected value of the number of tests taken.