An article in Fire Technology, 2014 (50.3) studied the effectiveness of sprinklers in fire control by the number of sprinklers that activate correctly. The researchers estimate the probability of a sprinkler to activate correctly to be 0.7. Suppose that you are an inspector hired to write a safety report for a large ballroom with 10 sprinklers. Assume the sprinklers activate correctly or not independently.

What is the probability that all of the sprinklers will operate correctly in a fire?

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Answer:

2.82% probability that all of the sprinklers will operate correctly in a fire

Step-by-step explanation:

For each sprinkler, there are only two possible outcomes. Either they will operate correctly, or they will not. The probability of a sprinkler operating correctly is independent of other sprinklers. So we use the binomial probability distribution to solve this question.

Binomial probability distribution

The binomial probability is the probability of exactly x successes on n repeated trials, and X can only have two outcomes.

[tex]P(X = x) = C_{n,x}.p^{x}.(1-p)^{n-x}[/tex]

In which [tex]C_{n,x}[/tex] is the number of different combinations of x objects from a set of n elements, given by the following formula.

[tex]C_{n,x} = \frac{n!}{x!(n-x)!}[/tex]

And p is the probability of X happening.

The researchers estimate the probability of a sprinkler to activate correctly to be 0.7.

This means that [tex]p = 0.7[/tex]

10 sprinklers.

This means that [tex]n = 10[/tex]

What is the probability that all of the sprinklers will operate correctly in a fire?

This is P(X = 10).

[tex]P(X = x) = C_{n,x}.p^{x}.(1-p)^{n-x}[/tex]

[tex]P(X = 10) = C_{10,10}.(0.7)^{10}.(0.3)^{0} = 0.0282[/tex]

2.82% probability that all of the sprinklers will operate correctly in a fire

The probability that all sprinklers will operate correctly in a fire is 0.028

How to determine the probability

The given parameters are:

p = 0.7 ---- the probability that a sprinkler to activate correctly

n = 10 --- the number of sprinklers

The probability that all sprinklers activate correctly is calculated as:

[tex]P(10) = p^n[/tex]

So, we have:

[tex]P(10) = 0.7^{10[/tex]

Evaluate

[tex]P(10) = 0.028[/tex]

Hence, the probability that all sprinklers will operate correctly in a fire is 0.028

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