Answer:
The probability that you will have exactly 4 failures in one hour = 0.0112
Step-by-step explanation:
Number of pumps = 10
Probability of failure for the pumps in an hour = 0.10
Probability required is the probability that 4 out of 10 pumps fail in an hour.
This is a binomial distribution problem
Binomial distribution function is represented by
P(X = x) = ⁿCₓ pˣ qⁿ⁻ˣ
n = total number of sample spaces = total number of pumps
x = Number of successes required = in this case, number of failure required = 4
p = probability of success = probability that a pump actually fails = 0.1
q = probability of failure = probability that a pump doesn't fail = 0.9
The wordings of the question seem to counter the definition of parameters in the formula, but it is the understanding that is key.
P(X=4) = ¹⁰C₄ (0.1)⁴ (0.9)¹⁰⁻⁴ = 0.011160261 = 0.0112