# 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 - Mathematics and Statistics

Sum

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

(i) none

(ii) not more than one

(iii) more than one

(iv) at least one

will fuse after 150 days of use.

#### Solution

Let X represent the number of bulbs that will fuse after 150 days of use in an experiment of 5 trials. The trials are Bernoulli trials.

It is given that, p = 0.05

∴ q = 1 - p = 1- 0.05 = 0.95

X has a binomial distribution with n = 5 and p = 0.05

∴ P (X = x) = "^nC_x  p^x  q^(n - x) where x = 1, 2, ....n

= "^5C_x (0.05)^x (0.95)^(n - x)

(i) P (none) = P(X = 0)

= p(0) = "^5C_0 (0.05)^0 (0.95)^(5 - 0)

= 1xx1 xx (0.95)^5

= (0.95)2

(ii) P (not more than one) = P(X ≤ 1)

= p(0) + p(1)

= ""^5C_0 *(0.05)^0 (0.95)^(5-0) + "^5C_1 (0.05)^1 (0.95)^4

= 1xx1 xx (0.95)^5 + 5 xx (0.05) xx (0.95)^4

= (0.95)^4 [0.95 + 5(0.05)]

= (0.95)^4 (0.95 + 0.25)

= (0.95)^4 (1.20) = (1.2)(0.95)^4

(iii) P (more than 1) = P(X > 1)

= 1 - P[X ≤ 1]

= 1 - (1.2)(0.95)4

(iv) P (at least one) = P(X ≥ 1)

= 1 - P[X = 0]

= 1 - p(0)

= 1 - "^5C_0 (0.05)^0 (0.95)^(5 - 0)

= 1 - 1 xx 1 xx (0.95)^5

= 1 - (0.95)^5`

Concept: Bernoulli Trials and Binomial Distribution
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#### APPEARS IN

NCERT Class 12 Maths
Chapter 13 Probability
Q 5 | Page 577