Source: Official Guide for GMAT Review 2016 Data Sufficiency ; #84

2

On a certain nonstop trip, Marta averaged

On a certain nonstop trip, Marta averaged x miles per hour for 2 hours and y miles per hour for the remaining 3 hours. What was her average speed, in miles per hour, for the entire trip?

1 Explanation

1

Jordan Song

Average speed = Total distance/Total time ;
Total distance = Avg speed * Total time

since D=RT
Marta averaged x miles per hour for 2 hours = 2x
y miles per hour for the remaining 3 hours = 3y
Total distance = 2x+3y
Total time = 2+3 = 5 hrs
Avg speed = 2x+3y/5

Statement (1):
2x+3y=280
Avg speed = 280/5 = 56m/h. Sufficient.

Statement (2):
y = x + 10, Not sufficient.
Plug y into 2x+3y/5, x still unknown

Answer is A

Apr 28, 2016 • Comment

Cydney Seigerman, Magoosh Tutor

Thanks for sharing your solution, Jordan! Great job :)

Apr 30, 2016 • Reply

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Official Guide for GMAT Review 2016

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Section 6.3 Data Sufficiency

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