Question

The probability that a bulb produced by a factory will fuse after 150 days of use is 0.05. What is the probability that out of 5 such bulbs none will fuse after 150 days of use

• A. $1 - \left( \frac { 19 } { 20 } \right) ^ { 5 }$
• B. $\left( \frac { 19 } { 20 } \right) ^ { 5 }$
• C. $\left( \frac { 3 } { 4 } \right) ^ { 5 }$
• D. $90 \left( \frac { 1 } { 4 } \right) ^ { 5 }$

Answer 1

Answer: (B)

$\left( \frac { 19 } { 20 } \right) ^ { 5 }$

Answer 2

Here $p = \frac { 19 } { 20 } , q = \frac { 1 } { 20 } , n = 5 , r = 5$

The required probability

$= { } ^ { 5 } C _ { 5 } \left( \frac { 19 } { 20 } \right) ^ { 5 } \cdot \left( \frac { 1 } { 20 } \right) ^ { 0 } = \left( \frac { 19 } { 20 } \right) ^ { 5 }$