An empty fuel tank with a capacity of 200 gallons was filled partially with fuel A and then to capacity with fuel B. Fuel A contains 12% ethanol by volume and fuel B contains 16% ethanol by volume. If the full fuel tank contains 20 gallons of ethanol, how many gallons of fuel A were added? Choose one:  A) 300  B) 150  C) 100  D) 80  E) 50
Say there are A gallons of fuel A in the tank, then there would be 200-A gallons of fuel B.   The amount of ethanol in A gallons of fuel A is 0.12A;   The amount of ethanol in 200-A gallons of fuel B is 0.16(200-A);   Since the total amount of ethanol is 20 gallons then 0.12A+0.16(200-A)=20 --&gt; A=300.   300nswer: 300.
<result>A</result>
An empty fuel tank with a capacity of 200 gallons was filled partially with fuel A and then to capacity with fuel B. Fuel A contains 12% ethanol by volume and fuel B contains 16% ethanol by volume. If the full fuel tank contains 20 gallons of ethanol, how many gallons of fuel A were added?