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Speed and distance

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by naaga » Thu Feb 12, 2009 7:09 am
9. What was John’s average driving speed in miles per hour during a 15-minute interval?
(1) He drove 10 miles during this interval.
(2) His maximum speed was 50 miles per hour and his minimum speed was 35 miles per hour during this interval.


can anyone help explanation
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Source: — Data Sufficiency |
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by DanaJ » Thu Feb 12, 2009 7:17 am
1 is insufficient since you do not know anything about his speed for the 10 mins. It could well have been 10 miles per hour or 100 miles per hour.

2 is insufficient because we do not know the average speed or how much he drove with 50 or 35. He could have driven 5 mins with 50 mile/h and 10 with 35m/h or the other way around.

Taken together both stmts don't help much, since you don't know anything else about the average speed.
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Re: Speed and distance

by billzhao » Thu Feb 12, 2009 7:18 am
naaga wrote:9. What was John’s average driving speed in miles per hour during a 15-minute interval?
(1) He drove 10 miles during this interval.
(2) His maximum speed was 50 miles per hour and his minimum speed was 35 miles per hour during this interval.


can anyone help explanation
From (1), we have: Average speed = Distance / Time = 10 miles / 0.25hours = 40 miles per hour. So (1) is sufficient. we will choose between A & D.

From (2), we cannot tell what is the average speed just based on the minimum and maximum speeds. So (2) is insufficient.

so my answer is (A)
Yiliang
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Original answer

by naaga » Thu Feb 12, 2009 7:24 am
OA is (A)
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by DanaJ » Thu Feb 12, 2009 7:49 am
Man I'm dumb.... We are looking for average speed... Sorry... I misunderstood the question.
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