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The time , in hours , it takes to repair an electrical breakdown in a certain factory is represent by a random variable x where repair time
Question
The time , in hours , it takes to repair an electrical breakdown in a certain factory is represent by a random variable x where repair time follow a normal distribution with mean 5 hour and standard deviation 1 hour , if 5 electrical breakdown ore randomly chosen , Find the probability that ( a all repaired time below 6 hours ( b ) exactly 3 of them repaired below 6 hours
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2021-09-01T03:17:58+00:00
2021-09-01T03:17:58+00:00 1 Answers
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Answers ( )
Answer:
a) 0.4215 = 42.15% probability that all are repaired in less than 6 hours.
b) 0.15 = 15% probability that exactly 3 of them repaired in a time below 6 hours
Step-by-step explanation:
To solve this question, we need to understand the normal and the binomial probability distributions.
Binomial probability distribution
The binomial probability is the probability of exactly x successes on n repeated trials, and X can only have two outcomes.
In which
is the number of different combinations of x objects from a set of n elements, given by the following formula.
And p is the probability of X happening.
Normal Probability Distribution:
Problems of normal distributions can be solved using the z-score formula.
In a set with mean
and standard deviation
, the z-score of a measure X is given by:
The Z-score measures how many standard deviations the measure is from the mean. After finding the Z-score, we look at the z-score table and find the p-value associated with this z-score. This p-value is the probability that the value of the measure is smaller than X, that is, the percentile of X. Subtracting 1 by the p-value, we get the probability that the value of the measure is greater than X.
Proportion repaired below 6 hours:
Mean 5 hours and standard deviation 1 hour, which means that
This proportion is the p-value of Z when X = 6. So
0.8413 repaired below 6 hours.
For the binomial distribution, this means that
5 are chosen:
This means that
a) Probability that all are repaired in less than 6 hours
This is P(X = 5). So
0.4215 = 42.15% probability that all are repaired in less than 6 hours.
b) Probability that exactly 3 of them repaired below 6 hours
This is P(X = 3). So
0.15 = 15% probability that exactly 3 of them repaired in a time below 6 hours