A company that mixes and sells concrete has a contract to deliver several loads of concrete containing an aggregate that is 20% sand by weight. (CONTINUED!)

Question

A company that mixes and sells concrete has a contract to deliver several loads of concrete containing an aggregate that is 20% sand by weight. the company has a pile that contains 360,000 lb if aggregate that is 15% sand. How much sand will be required to mix with the aggregate in this pile to produce a picture that is 20% sand?

Answer 1

Let s be the amount of sand to added.

 

The pile that has 15% sand contains .15(360000) = 54000 pounds of sand.

 

With the sand added the total weight of concrete would be 360000 + s.

This final mixture would contain 20% sand.

 

This means .2(360000 + s) = 54000 + s

                   72000 + ,2s = 54000 + s

                    .8s = 18000

                   s = 22500 pounds of sand must be added