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# M20-36

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Math Expert
Joined: 02 Sep 2009
Posts: 46991

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16 Sep 2014, 01:09
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Difficulty:

5% (low)

Question Stats:

92% (00:28) correct 8% (01:02) wrong based on 108 sessions

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If Sarah drove at 50 kmh during the first hour of her trip and at 80 kmh during the second and third hour, what was Sarah's average speed for the three-hour trip?

A. 65 kmh
B. 68 kmh
C. 70 kmh
D. 72 kmh
E. 75 kmh

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Math Expert
Joined: 02 Sep 2009
Posts: 46991

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16 Sep 2014, 01:09
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Official Solution:

If Sarah drove at 50 kmh during the first hour of her trip and at 80 kmh during the second and third hour, what was Sarah's average speed for the three-hour trip?

A. 65 kmh
B. 68 kmh
C. 70 kmh
D. 72 kmh
E. 75 kmh

Sarah went $$50*1 + 80*2 = 210$$ kilometers in 3 hours. Thus, her average speed was $$\frac{210}{3} = 70$$kmh.

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Joined: 08 Jun 2015
Posts: 519
Location: India
GMAT 1: 640 Q48 V29
GMAT 2: 700 Q48 V38

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01 Nov 2017, 05:35
Option C. Avg speed is total distance divided by total time. (50+80+80)/3. That comes to 210/3 or 70Kmph.
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Re: M20-36   [#permalink] 01 Nov 2017, 05:35
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# M20-36

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