If a tank has x gallons, then....
On the highway you're getting 462/x mpg
In the city you're getting 336/x mpg
With 6 fewer mpg in the city, then 462/x - 336/x = 6 Multiply both sides by x.....
462 - 336 = 6x
126 = 6x
21 = x That's in the answer choices as (C), as a TRAP.
Your city mpg is 336/x, so that's 336/21 = 16. Answer choice (B).
I would also add this would be a good Backsolving problem. And if you're running out of time and have to make a strategic guess, figure there will probably be some trap answer that represents HIGHWAY mpg's, so odds are the right answer will be 6 smaller than another answer choice. The only answers here that fit that description are (B) (which is 6 smaller than D), and (C) (which is 6 smaller than E).
Gene Suhir
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