To clean a tank, 3/4 cup of disinfectant is needed for every 2 gallons of water. how many cups of disinfectant are needed for 20 gallons of water?
a. 7 1/2
b. 15
c. 22 1/2
d. 30

Understand the concept of a unit rate a/b associated with a ratio a:b with b ≠ 0, and use rate language in the context of a ratio relationship. For example, “This recipe has a ratio of 3 cups of flour to 4  cups of sugar, so there is 3/4 cup of flour for each cup of gallons of water.”How many cups of disinfectant are needed for 20 gallons of water so c is 

I use ratio and proportion changes 3/4= .75 .75 cups/2 gallons= x cups/2o gallons cross multiply 2x= 15 x= 7 1/2 cups also there are 10 gallons for every 3/4 cup 10 x 3/4= 30/4= 7 1/2 I like ratio and proportion it's more consistent in solving lots of problems hope this helps