How can you solve this answer a school cafeteria makes cheese sauce for macaroni using 15 cups of swiss cheese and 17 cups of cheddar cheese perry tries to make the sauce for a family party using 5 cups of swiss and 7 cups of cheddar ,is perry using the correct ratio

The fastest and easiest way to check if two ratios are equivalent is to cross multiply. 
1) 15:17
2) 5:7 

set it up with the first number of one ratio being multiplied by the second number of the other ratio, e.g., 
a) 15 x 7
b) 5 x 17 

the two products you get are 105, and 85, respectively. 

Since the two products differ, these ratios are not equivalent