How much water should be added to 30 gallons of a solution that is 70% antifreeze
in order to get a mixture that is 60% antifreeze?
Since water is added to the solution, we must think in terms of water.
The original solution is 30 gallons which is 30% water.
. . It contains: gallons of water.
Then gallons of water is added.
The final mixture contains: gallons of water. .
But we know that the final mixture will be gallons which is 40% water.
. . It contains: gallons of water. .
We just described the final amount of water in two ways.
There is our equation! . . .