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M21-31

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Joined: 02 Sep 2009
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16 Sep 2014, 00:15
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Difficulty:

15% (low)

Question Stats:

80% (00:42) correct 20% (00:45) wrong based on 106 sessions

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If during the first two hours of its four-hour trip, a car went at a constant speed of 75 kmh, what was the average speed of the car for the entire trip?

(1) During the last two hours of the trip, the car traveled 10 km further than during the first two hours

(2) The average speed of the car during the last two hours of the trip was 80 kmh

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16 Sep 2014, 00:15
Official Solution:

Statement (1) by itself is sufficient. During the first two hours, the car covered $$75*2 = 150$$ km. During the last two hours, it covered $$150 + 10 = 160$$ km. Average speed = $$\frac{150 + 160}{4} = 77.5$$.

Statement (2) by itself is sufficient. During the first two hours, the car covered $$75*2 = 150$$ km. During the last two hours, it covered $$80*2 = 160$$ km. Average speed $$= \frac{150 + 160}{4} = 77.5$$.

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15 Dec 2017, 08:28
+1 for D. Avg speed is total distance/ total time taken. We need to find the total distance and then the total time which is given to be four hours. Both statement 1 and statement 2 are individually sufficient to find the average speed. Hence option D.
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Re: M21-31 &nbs [#permalink] 15 Dec 2017, 08:28
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