# Moderate Probability Solved QuestionAptitude Discussion

 Q. The probability that a student is not a swimmer is 1/5. Then the probability that one of the five students, four are swimmers is:
 ✖ A. $^5C_4\left(\dfrac{4}{5}\right)^2\left(\dfrac{1}{5}\right)$ ✖ B. $\left(\dfrac{4}{5}\right)^2\left(\dfrac{1}{5}\right)$ ✔ C. $^5C_4\left(\dfrac{1}{5}\right)\left(\dfrac{4}{5}\right)^4$ ✖ D. None of these

Solution:
Option(C) is correct

4 students out of 5 can be selected in $^5C_4$ ways.

Probability of a student being not a swimmer $=\dfrac{1}{5}$

Probability of a student being a swimmer

$=1-\left(\dfrac{1}{5}\right)=\dfrac{4}{5}$

Required probability

$=^5C_4\times\left(\dfrac{1}{5}\right)\times \left(\dfrac{4}{5}\right)^4$

## (3) Comment(s)

Gaurav Karnani
()

question language has ambiguity

Sudeep Sahu
()

can anyone explain me this problem in more detail....?

Jyothi
()

its based on a formula ncr*(p)^r(1-p)^n-r

p= probability of favourable outcomes

n= total events

r=favorable events