Answer:
The minimum number of books that should be tested is 312.
Step-by-step explanation:
The (1 - <em>α</em>)% confidence interval for population mean (<em>μ</em>) is:

The margin of error for this interval is:

The information provided is:
MOE = 0.10
<em>σ</em> = 0.90
Confidence level = 95%
Compute the critical value of <em>z</em> as follows:

*Use a <em>z</em>-table.
Compute the value of <em>n</em> as follows:

![n=[\frac{z_{\alpha/2}\times \sigma}{MOE} ]^{2}](https://tex.z-dn.net/?f=n%3D%5B%5Cfrac%7Bz_%7B%5Calpha%2F2%7D%5Ctimes%20%5Csigma%7D%7BMOE%7D%20%5D%5E%7B2%7D)
![=[\frac{1.96\times 0.90}{0.10}]^{2}](https://tex.z-dn.net/?f=%3D%5B%5Cfrac%7B1.96%5Ctimes%200.90%7D%7B0.10%7D%5D%5E%7B2%7D)

Thus, the minimum number of books that should be tested is 312.