Question

1. Serena is in a math class of 20 students. Each day for a week (Monday to Friday), a student in Serena’s class is

randomly selected by the teacher to explain a homework problem. Once a student’s name is selected, that student
is not eligible to be selected again that week.
a. What is the probability that Serena is selected on Monday?
b. What is the probability that Serena is selected on Tuesday given that she was not selected on Monday?
c. What is the probability that she will be selected on Friday given that she was not selected on any of the other days?

Answer 1

a) 0.05

b) 0.0526

c) 0.0625

Explanation:

Data provided in the question:

Total number of students in a class = 20

a) since it is Monday, no student will be selected already.

Therefore,

There are 20 students from which one can be selected

Thus,

P(Serena is selected on Monday) = 1 ÷ [Number of students available]

= 1 ÷ 20

= 0.05

b) On Tuesday, one student has already been selected on Monday

Therefore,

There are (20 - 1) = 19 students from which one can be selected

Thus,

P(Serena is selected on Tuesday) = 1 ÷ [Number of students available]

= 1 ÷ 19

= 0.0526

c) On Friday , 4 student has already been selected on Monday

Therefore,

There are (20 - 4) = 16 students from which one can be selected

Thus,

P(Serena is selected on Tuesday) = 1 ÷ [Number of students available]

= 1 ÷ 16

= 0.0625