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If John traveled a trip at a constant rate 20 miles per hour

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If John traveled a trip at a constant rate 20 miles per hour

by Max@Math Revolution » Sat Oct 01, 2016 12:59 am
If John traveled a trip at a constant rate 20 miles per hour for 30 minutes and at a constant rate 30 miles per hour for the remaining 20 minutes, what is the his average speed, in miles per hour?
A. 20miles B. 24miles C. 30miles D. 32miles E. 36miles
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by DavidG@VeritasPrep » Sat Oct 01, 2016 3:22 am
Max@Math Revolution wrote:If John traveled a trip at a constant rate 20 miles per hour for 30 minutes and at a constant rate 30 miles per hour for the remaining 20 minutes, what is the his average speed, in miles per hour?
A. 20miles B. 24miles C. 30miles D. 32miles E. 36miles

First part of the trip: 20mph for 1/2 hour: 10 miles traveled.
Second part of the trip: 30mph for 1/3 hour: 10 miles traveled.

Total travel time = 50 minutes or 5/6 of an hour.
Total distance covered = 20 miles

R * T = D
R * 5/6 = 20
R = 24; answer is C
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by DavidG@VeritasPrep » Sat Oct 01, 2016 3:23 am
Max@Math Revolution wrote:If John traveled a trip at a constant rate 20 miles per hour for 30 minutes and at a constant rate 30 miles per hour for the remaining 20 minutes, what is the his average speed, in miles per hour?
A. 20miles B. 24miles C. 30miles D. 32miles E. 36miles
Or just use some basic logic. The average speed will have to fall between 20 and 30. Only C works.
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by Max@Math Revolution » Sun Oct 02, 2016 11:59 pm
==> Average speed=the sum of distances/the sum of hours taken
John travelled 10 miles because he travelled at 20 mph for 30 minutes, and also travelled another 10 miles since he travelled at 30mph for 20 minutes. This leads to
Average Speed = (10miles+10miles)/(30min.+20min.)=24miles/1hour
Therefore, the answer is B.

Answer: B
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