Question

A 500-page book contains 250 sheets of paper. The thickness of the paper used to manufacture the book has mean 0.08 mm and standard deviation 0.01 mm. What is the probability that a randomly chosen book is more than 20.2 mm thick (not including the covers)

Answer 1

Answer:

10.20% probability that a randomly chosen book is more than 20.2 mm thick

Step-by-step explanation:

Problems of normally distributed samples are solved using the z-score formula.

In a set with mean $\mu$ and standard deviation $\sigma$, the zscore of a measure X is given by:

$Z = \frac{X - \mu}{\sigma}$

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 pvalue, we get the probability that the value of the measure is greater than X.

In this problem, we have that:

250 sheets, each sheet has mean 0.08 mm and standard deviation 0.01 mm.

So for the book.

$\mu = 250*0.08 = 20, \sigma = \sqrt{250}*0.01 = 0.158$

What is the probability that a randomly chosen book is more than 20.2 mm thick (not including the covers)

This is 1 subtracted by the pvalue of Z when X = 20.2. So

$Z = \frac{X - \mu}{\sigma}$

$Z = \frac{20.2 - 20}{0.158}$

$Z = 1.27$

$Z = 1.27$ has a pvalue of 0.8980

1 - 0.8980 = 0.1020

10.20% probability that a randomly chosen book is more than 20.2 mm thick