Question

A class has 20 students. If the teacher is randomly selecting a group of 3 students to represent the class on the student council, what is the probability that Sarah and her two best friends will all be chosen?

1/20
3/20
1/1,140

Answer 1

Answer is C. 1/1,140

Answer 2

P(Sarah and her two best friends will all be chosen)=1/1140

Explanation:

A class has 20 students.

The teacher is randomly selecting a group of 3 students to represent the class on the student council.

The number of ways of choosing 3 students out of 20=
`20_{C_(3)}`

= 1140

we have to find the probability that Sarah and her two best friends will all be chosen.

That means Sarah and her friends are one group to be chosen.

Hence, P(Sarah and her two best friends will all be chosen)=1/1140