ladyrenee95 wrote:

A certain car travels 18 miles per gallon of gas on city streets and 30 miles per gallon of gas on highway. Damaris drives the car to work during the week and travels on city streets and on the highway. She drives the car on the highway more miles than she drives on city streets. How many miles does Damaris drive to work on the highway?

(1) Damaris drives a total of 26 miles.

(2) The car Damaris drives uses 1 gallon of gas to get to work.

Source: Ready4GMAT app

hi

there are TWO averages 18/gallon and 30/gallon

(1) Damaris drives a total of 26 miles.

we cannot say anything

insuff

(2) The car Damaris drives uses 1 gallon of gas to get to work.

again insuff

combined

we can get the ratio of distance traveled on both routes

suff

C

solution

(1) weighted average..so we can say two averages 18 and 30 .. and final average 26..

so gallons used on route 30/gallon = \(\frac{26-18}{30-18} = \frac{8}{12} = \frac{2}{3}\)

distance traveled = \(30*\frac{2}{3} = 20\)

(2) second methodlet x distance be traveled on highway, so 26-x will be traveled on streets..

gallons used =\(1 = \frac{x}{30} + \frac{26-x}{18} ............\frac{90 = 3x+130-5x}{90}........2x=40...x=20\)

_________________

1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372

2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html

3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html

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