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Re: Bob just filled his car's gas tank with 20 gallons of gasoho [#permalink]
Something doesn't quite add up in my head. You have to go to get a pen and a sheet of paper to try to calculate it manually, not in the head.
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Re: Bob just filled his car's gas tank with 20 gallons of gasoho [#permalink]
Put weight average formula here to get easy solution.

For such issues just consider one element either ethanol or another one, I took ethanol because our focus is to add more ethanol in the gallon unit.

let's think he needs x gallons of ethanol to reach 10 percent of ethanol to perform well in his car.

x= weight of amount X total amount

A= 20 X 0.05 = 1 gallon

Here, \(\frac{(20 * 0.05 + x)}{(20+x)}\) = \(\frac{10}{100}\)
=> 1 + x = 2 + 0.1
=> x = \(\frac{10}{9}\)

so, the answer is C
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Re: Bob just filled his car's gas tank with 20 gallons of gasoho [#permalink]
Hello from the GRE Prep Club BumpBot!

Thanks to another GRE Prep Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: Bob just filled his car's gas tank with 20 gallons of gasoho [#permalink]
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