The probability that the number of tested rafts that develop cracks is no more than 3 is <u>.00006</u>.
The true proportion, p for the population is given to 0.12.
Thus, the mean, μ, for the sample = np = 27*0.12 = 3.24.
The sample size, n, given to us is 27.
Thus, the standard deviation, s, for the sample can be calculated using the formula, s = √{p(1 - p)}/n.
s = √{0.12(1 - 0.12)}/27 = √0.003911 = 0.0625389.
We are asked to calculate the probability that the number of tested rafts that develop cracks is no more than 3, that is, we need to calculate P(X ≤3).
P(X ≤ 3)
= P(Z ≤ {(3 - 3.24)/0.0625389) {Using the formula z = (x - μ)/s}
= P(Z ≤ -3.8376114706)
= .00006 {From table}.
Thus, the probability that the number of tested rafts that develop cracks is no more than 3 is <u>.00006</u>.
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