How much orange juice at 42¢ a liter should be mixed with grapefruit juice worth 32¢ a liter to make 200 liters of a mixture worth 36¢ a liter?

80 liters of orange juice must be mixed.

Explanation

Lets assume, the amount of orange juice is liters.

As the amount of mixture is 200 liters, so the amount of grapefruit juice will be:

Price of orange juice = 42¢ /liter , price of grapefruit juice = 32¢ /liter and the price of mixture = 36¢ /liter

So,  total price of liters orange juice ¢ ,

total price of liters grapefruit juice ¢  and

total price of 200 liters mixture ¢

Thus the equation will be ....

So, the amount of orange juice to be mixed is 80 liters.