Pretty simple question but would like to know the quickest way to solve.

How many factors of 3 are between -100 and 100?

Do you mean how many multiples of 3 are there between -100 and 100?

First, consider the positive multiples of 3: 3, 6, 9, ..., 96, 99. Divide 99 by 3 to get 33.
There are just as many negative ones, or 33 more, to give a running total of 66.
Add one more for zero, which is a multiple of every number, to give a final total of 67.


If you did mean how many factors of 3 are there between -100 and 100, then the answer is 4: -3, -1, 1, and 3.