3. the diameter of the large bird bath is 6 feet. the cgj girls plan to put bird perches around the outside edge of the bath such that there is at least 3 feet between the perches. at most, how many perches will they be able to install?

First we need to determine the circumference of the bath.

Circumference = Diameter X pi 

6(pi) = 18.84 feet

and the girls want to put perches that are at least 3 feet between each other so you can just divide the circumference by 3 

18.84 / 3 = 6.28 so 6

If you don't understand the concept then think of it like this, if you have in total 18.84 feet and you want to place something down every 3 feet then start subtracting 3 from your total till you can't add anymore perches. 

18 - 3 = 15
15 - 3 = 12
12 - 3 = 9
9 - 3 = 6
6 - 3 = 3
3 - 3 = 0

We subtracted 3, SIX times so we added 6 perches