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Question: If the probability of getting II and III division of a student is respectively \(\frac { 1 } { 3 }\...

If the probability of getting II and III division of a student is respectively 13\frac { 1 } { 3 } and 15\frac { 1 } { 5 }. If he never fails then the probability of getting 1st division , is

A

8/15

B

7/15

C

1/15

D

1/5

Answer

7/15

Explanation

Solution

Getting of 1st, 2nd, 3rd division is exhaustive and

mutually exclusive

P(I Č II Č III) = 1

P(I) + P(II) + P(III) = 1

P(I) = 1 – P(II) – P(III) = 1 – 15\frac { 1 } { 5 }=15−5−315\frac { 15 - 5 - 3 } { 15 }= 715\frac { 7 } { 15 }