Aptitude 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

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

**Gaurav Karnani**

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**Sudeep Sahu**

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

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

p= probability of favourable outcomes

n= total events

r=favorable events

question language has ambiguity