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Susan drove an average speed of 30 miles per hour for the

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Susan drove an average speed of 30 miles per hour for the [#permalink]

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New post 27 Feb 2018, 22:38
anilnandyala wrote:
Susan drove an average speed of 30 miles per hour for the first 30 miles of a trip & then at a average speed of 60 miles/hr for the remaining 30 miles of the trip if she made no stops during the trip what was susan's avg speed in miles/hr for the entire trip

A. 35
B. 40
C. 45
D. 50
E. 55

IMO B .i solved this question by box method attached bellow:-
KUDOS iF YOU LIKE MY EXPLANATION. THANKS IN ADVANCE
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Re: Susan drove an average speed of 30 miles per hour for the [#permalink]

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New post 03 Apr 2018, 10:19
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anilnandyala wrote:
Susan drove an average speed of 30 miles per hour for the first 30 miles of a trip & then at a average speed of 60 miles/hr for the remaining 30 miles of the trip if she made no stops during the trip what was susan's avg speed in miles/hr for the entire trip

A. 35
B. 40
C. 45
D. 50
E. 55


Average speed = (TOTAL distance)/(TOTAL time)

TOTAL distance
Susan traveled 30 miles at a speed of 30mph, and 30 miles more at a speed of 60mph.
So, TOTAL distance = 30 miles + 30 miles = 60 miles

TOTAL time
TOTAL time = (time spent driving 30 mph) + (time spent driving 60 mph)
time = distance/speed
- Time spent driving 30 mph = 30 miles/30mph = 1 hour
- Time spent driving 60 mph = 30 miles/60mph = 0.5 hours
TOTAL time = (1 hour) + (0.5 hours) = 1.5 hours
----------------------------------

So, Average speed = (TOTAL distance)/(TOTAL time)
= 60 miles/1.5 hours
= 40 mph

Answer: B

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Brent
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Re: Susan drove an average speed of 30 miles per hour for the [#permalink]

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New post 14 Apr 2018, 23:04
anilnandyala wrote:
Susan drove an average speed of 30 miles per hour for the first 30 miles of a trip & then at a average speed of 60 miles/hr for the remaining 30 miles of the trip if she made no stops during the trip what was susan's avg speed in miles/hr for the entire trip

A. 35
B. 40
C. 45
D. 50
E. 55


Distance 1 = 30 miles

Speed 1 = 30 m/h

Time 1 = 30/30 = 1 hr

Distance 2 = 30 miles

Speed 2 = 60 m/h

Time 2 = 30/60 = 0.5 hr

Average speed = \(\frac{30 * 1 + 60 * 0.5}{1 + 0.5}\)

Avg Speed = 40 m/h

(B)
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Re: Susan drove an average speed of 30 miles per hour for the   [#permalink] 14 Apr 2018, 23:04

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