GMAT Q please help

[ddo]

Could you help me with this question, it was very easy but somehow didnt work.. I won't be able to sleep thinking on it.

A truck consumes 10 gallons gas per mile when driven in the city and 25 gallons gas per mile when driven in the highway. If it was driven 20 miles in the city and 30 miles in the highway, which of he following is the closest to its total average consumption?

a.16
b.18
c.20
D and E dont remeber but higher than 20.

I did (10*20 + 25*30)/30+20 = 19... but it was not an option!!!! the "closest" options were 18 and 20.. so which is the right one?

[VP_Jim]

Are you sure the question said "gallons per mile" and not "miles per gallon"?

My guess is that it said "miles per gallon", which would make the answer 16.

It would have used 2 gallons in the city to drive 20 miles, and a little over 1 gallon on the highway to drive 30 miles. So, it went 50 miles and used a little over 3 gallons of gas. 50/3 is about 16.

[niraj_a]

VP_jim,

i followed the same method as the thread author. why would that be incorrect?

[ddo]

Hi Niraj

Yes, it would be incorrect, you will get 19 instead of 16.

Thanks JIM!