How many quarts of pure antifreeze must be added to 20 quarts of a 45% antifreeze solution to obtain a 75% antifreeze solution?

24 quarts

Step-by-step explanation:

45% of 20 is 0.45 * 20 = 9

So in 20 quarts, 9 is pure antifreeze

suppose we want to add x quarts and this will make it 75%. So we can write:

Now we cross multiply, do algebra, and solve for x:

Hence, 24 quarts should be added