proportions

Question

A recipe calls for 3/8 ounce almonds to make two servings. How many ounces of almonds do you need to make 25 servings?

Answer 1

It takes 3/8 oz. to make two servings, and we need to find out how many ounces will produce 25 servings. Call that unknown quantity x. Then we can write the following:

 

3/8   =   x  

  2         25

 

To solve for x, we can cross-multiply.

 

2x = 25 (3/8) = 25/1 * 3/8 = 75/8

 

If 2x = 75/8, can you now solve for x?

Answer 2

The proportion is a good way to look at this as

Michael A. and Mark M. demonstrated.  Also we 

can check by what factor the servings changed

and change the ounces by the same factor

 

2x = 25

x = 25/2

 

Servings went up by a factor of 25/2

so multiply the ounces by 25/2

 

(3/8)(25/2) = 75/16 = 4 11/16 ounces

 

This is really the same thing the other two

excellent tuors did.  Just another way of

thinking about it.

Answer 3

3/8 : 2 :: x : 25         proportion

2x = (3/8)(25)           product means/extremes

2x = 75/86               

x = 75/16