Proportional ratio

Question

To make a pie, Jamie needs to put in a ratio of 3/8 of a cup of sugar for every 2 1/4 cups of flour. How many cups of sugar would Jamie need for every 1 cup of flour?

Answer 1

Hi Kristen,

 

You can solve this by setting up ratios:  3/8 cup sugar is to 2 1/4 cups flour as X cups sugar is to 1 cup flour.

 

You can write this mathematically as:  (3/8) / (2 1/4) = X / 1

 

Now cross multiply (top of one fraction times bottom of the other)--> 3/8 = (2 1/4)X

 

Change the mixed fraction into an improper fraction--> 3/8 = 9X / 4

 

Cross multiply again--> 12 = 72X

 

Divide both sides by 72--> X = 1/6 cup

 

Dan

Answer 2

The ratio of sugar to flour remains constant.  Let x=number of cups of sugar

 

            (cups of sugar) / (cups of flour)  =  (3/8 cup of sugar) / (2 1/4 cups of flour)  = x / (1 cup of flour)

 

      x = (3/8) / (2 1/4)

      x = (3/8) / (9/4)                  [use improper fraction]

      x = (3/8) * (4/9)                  [ invert denominator and multiply]

      x = (12/72)

      x = (1/6)

 

Jamie needs 1/6 cup of sugar for every 1 cup of flour.