abhirup1711 wrote:Bob just filled his car's gas tank with 20 gallons of gasohol, a mixture consisting of 5% ethanol and 95% gasoline. If his car runs best on a mixture consisting of 10% ethanol and 90% gasoline, how many gallons of ethanol must he add into the gas tank for his car to achieve optimum performance?
a) 9/10
b) 1
c) 10/9
d) 20/19
e) 2
Current amount of ethanol = .05(20) = 1 gallon.
We can plug in the answers, which represent the amount of ethanol that must be added to yield a 10% solution.
Answer choice C: 10/9 gallons
New ethanol = current ethanol + 10/9 = 1 + 10/9 = 19/9.
New total = current total + 10/9 = 20 + 10/9 = 190/9.
Result:
(new ethanol)/(new total) = (19/9) / (190/9) = 1/10 = 10%.
Success!
The correct answer is
C.
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