Bunuel wrote:

Jason drives to his parents' house and back home the same way. On the way to his parents' house, his speed is 10 kilometers per hour slower than his speed on his way back, and therefore it takes him 20 minutes longer. If Jason drives to his parents' house at 50 kilometers per hour, how many minutes does he spend on his way back from his parents' house?

A. 60

B. 80

C. 100

D. 120

E. 150

Speed on way to parents house 50.... so time taken is x/50 where x is the distance..

On way back it is x/(50+10)=x/60..

So x/50 -x/60 =1/3....x/300=1/3..x=100km...

Time on way back = 100/60 hr or 100*60/60=100 minutes

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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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