Walter is mixing cement for his new patio. he knows he needs to water-to-cement ratio of 20-30. what percent of his total mixture is water?

The ratio of water to cement is 20:30 meaning that for every 20 parts of water, we have 30 parts of cement. There are 20+30 = 50 parts total.

Divide the number of parts of water (20) over the total number of parts (50)
20/50 = 2/5 = 0.40
use a calculator or long division to find the decimal form of 2/5 to be 0.40

Then move the decimal point 2 spots to the right to go from 0.40 to 40%

the percent of water in the mix is 40%