Maggie wrote

Don has 10% ethanol gasoline and 50% ethanol gasoline. If a customer wants 800 liters of 25% ethanol gasoline, how many liters of 10% and 50% ethanol must be mixed?

x = liters of 10% ethanol

800 - x = liters of 50% ethanol 800 liters in total

0.1x + 0.5(800 - x) = 0.25(800)

0.1x + 400 - 0.5x = 200 percent liters times number of liters equals total in mixture

-0.4x + 400 = 200 combined like terms

-0.4x = -200 subtracted 400

x = 500 divided by -0.4

800 - x = 300 substituted 500, in for x, into (800 - x)

500 liters of 10% ethanol

300 liters of 50% ethanol

*McGenius*