Jason drives to his parents' house and back home...

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BTGmoderatorLU: Moderator; Posts: 2650; Joined: Sun Oct 15, 2017 1:50 pmFollowed by: 6 members

by BTGmoderatorLU » Mon Jan 29, 2018 6:26 am

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

The OA is C.

I'm confused with this PS question. Experts, any suggestion about how can I solve it?

Can I say that he drives back from his parents' house at 40 kilometers per hour? then

The total time on his way back will be, t+20. I stuck here. Any expert help me, please? Thanks in advance.

Source: Beat The GMAT — Problem Solving | Mon Jan 29, 2018 6:26 am

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8246; Joined: Sat Apr 25, 2015 10:56 amFollowed by: 29 members; Location: Los Angeles, CA; Thanked: 43 times

hi

by Scott@TargetTestPrep » Wed Jan 31, 2018 4:23 pm

LUANDATO 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

The speed on the way to his parents’ house is 50 kmph; so the speed on the way back is 60 kmph.

If we let the distance each way = d, then d/50 = the time it takes to get to his parents house and d/60 = the time it takes him to get back home. Noting that 20 minutes =1/3 hour, we can create the equation:

d/50 - 1/3 = d/60

Multiplying by 300 we have:

6d - 100 = 5d

d = 100

The one-way distance is 100 miles, so the time spent coming back home is 100/60 hours, or 1 2/3 hours, or 100 minutes.

Answer: C

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