An animal shelter categorizes donors based on their yearly donation, as shown in the table

Question

Libby donated $50 during the first month of the year. If she makes three additional donations of equal amounts during the year, how much will she need to be in the silver category?

Answer 1

Let's call the required total donation for the silver category S, and the additional equal donations D.

Then we have 50 + 3D = S.

If S is known, we can solve for D as:

3D = S - 50

D = (S - 50) / 3