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Question: The probability that a teacher will give an unannounced test during any class is 1/5. If a student i...

The probability that a teacher will give an unannounced test during any class is 1/5. If a student is absent twice, then the probability that he misses atleast one test is

A

2/5

B

4/5

C

7/25

D

9/25

Answer

9/25

Explanation

Solution

Required probability

= 1 – P (student does not miss any test)

= 1 – P (the teacher does not give test on both days)

= 1 - (1−15)(1−15)=1−1625=925\left( 1 - \frac { 1 } { 5 } \right) \left( 1 - \frac { 1 } { 5 } \right) = 1 - \frac { 16 } { 25 } = \frac { 9 } { 25 } .