SOLUTION
Step 1 :
In this question, we are told that :
A book editor was proofreading a draft of a novel.
She found that the number of errors on each page of the book was normally distributed, with the mean number of errors on a page as 8 and a standard deviation of 1.
If 82 pages had between 7 and 9 errors.
We are meant to find the approximate total number of pages in the book.
Step 2 :
[tex]\begin{gathered} \text{Let the total number of pages be x,} \\ Z_9\text{ =}\frac{9-8}{1}\text{ = 1} \\ Z_{7\text{ }}\text{ = }\frac{7\text{ -8}}{1}\text{ = -1} \end{gathered}[/tex][tex]\text{Percentage ( Z}_7-Z_9)\text{ = }\frac{68.\text{ 2}}{100}\text{ of x = 82}[/tex][tex]\begin{gathered} x\text{ =}\frac{82}{0.682} \\ \text{x = 120.2} \\ x\text{ }\approx\text{ 120 pages} \end{gathered}[/tex]
CONCLUSION:
The approximate total number of pages in the book = 120 pages.
