Suppose a car can run on ethanol and gas and you have a 15 gallons tank to fill. You can buy fuel that is either 30 percent ethanol or 80 percent ethanol. How much of each type of fuel should you mix so that the mixture is 40 percent ethanol?
A method that I found online tells me to do the following.
Let A = amount
0.30A = ethanol amount
0.80(15 - A) = gas
Equation:
0.30A + 0.80(15 - A) = 0.40(15)
1. What does (15 - A) represent?
2. Why must 0.40 be multiplied by 15?
I don't get it.
