pappueshwar 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?
i thought the answer to be as 1 but its nt that way .request to explain
9/10
1
10/9
20/19
2
Current amount of ethanol = (.05)20 = 1.
We can plug in the answers, which represent the amount of ethanol that needs to be added.
Start with the middle answer choice.
If 10/9 doesn't work, we'll be able to see whether more or less ethanol is needed.
Answer choice C: 10/9
New amount of ethanol = 1 + 10/9 = 19/9.
New total of gasohol = 20 + 10/9 = 190/9.
New ethanol/new total = (19/9) / (190/9) = 19/190 = 1/10 = 10%.
Success!
The correct answer is
C.
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