Math proportions

Question

A recipe for spaghetti requires four 16-ounce bottles of ketchup to make 2 gallons of sauce. How many bottles of ketchup are needed to make 18 gallons of sauce?

Answer 1

 

Let x - number of bottles needed to make 18 gallons of sauce

 

bottles = 4 =  x       cross multiply

gallons    2   18

 

              2x = 72   divide by 2

                x = 36 bottles