Here are Xavier's bowling scores: Skip
135, 140, 130, 190, 112, 200, 185, 172, 163, 151,
149
What is the standard deviation rounded to the
nearest tenth?

A rate is something per one unit. To find a rate it is the total work done or how much is received divided by how long it took or how much you earn. Basically you divide by the per "blank" that you are trying to find. This will ensure that the "per" is one.

A. For this one the total work is the number of pages read. The "per" you are trying to find is hours ap you will divide number of pages read by number of hours it took.
15 pages/2 hours = 7.5 pages per hour

B. For this question the received is how much money and the "per" is page. This means you will divide total money earned by the number of pages proofread.
$40/15pages = $2.67 per page.

I really hope this helps! If you have any questions, feel free to ask, and I can try to help!