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On a journey across Dhaka, a bus averages 10 miles/h for 20% of the

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New post 01 Feb 2017, 09:04
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On a journey across Dhaka, a bus averages 10 miles/h for 20% of the distance, 30 miles/h for 60% of it and 20 miles/h for the remainder. What is the average speed for the whole journey?

(A) 10mph
(B) 30mph
(C) 5 mph
(D) 20 mph
(E) 25 mph

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Re: On a journey across Dhaka, a bus averages 10 miles/h for 20% of the  [#permalink]

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New post 01 Feb 2017, 09:50
lmuenzel wrote:
On a journey across Dhaka, a bus averages 10 miles/h for 20% of the distance, 30 miles/h for 60% of it and 20 miles/h for the remainder. What is the average speed for the whole journey?

(A) 10mph
(B) 30mph
(C) 5 mph
(D) 20 mph
(E) 25 mph



Avg. speed = total distance/ total time

Let total distance be X
As distance is divided into three parts 20% , 60% and again 20%
means distance of three part journey will be 20% of X = 20X/100 =X/5
and 60% of X = 60X/100 = 3x/5

avg speed = X / (x/(5*10) + x/ (3X/5*30) + X/ (5*20))
taking x common from dinominator and cancelling
we get Avg. speed =20mph

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Re: On a journey across Dhaka, a bus averages 10 miles/h for 20% of the  [#permalink]

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New post 01 Feb 2017, 10:15
Assume total distance = 100 miles
for 10miles/hr - its 20 miles in 2 hrs
for 30 miles/hr - its 60 miles in 2 hrs
for 20 miles/hr - its 20 miles in 1 hr
hence, total 100 miles in 5 hrs. therefore avg speed 20 miles/hr
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Re: On a journey across Dhaka, a bus averages 10 miles/h for 20% of the  [#permalink]

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New post 01 Feb 2017, 10:19
lmuenzel wrote:
On a journey across Dhaka, a bus averages 10 miles/h for 20% of the distance, 30 miles/h for 60% of it and 20 miles/h for the remainder. What is the average speed for the whole journey?

(A) 10mph
(B) 30mph
(C) 5 mph
(D) 20 mph
(E) 25 mph


Hi

Another way, slightly easier ..

Total TIME:-
Let the 100%=100 miles..
So 20% @10mph= 20 miles@10mph, so 20/10 or 2 hr
20%20 mph=20 miles20 mph so 20/20=1hr
60%@30 mph=60 miles@30 mph, so 60/30=2hr..
Total=2+1+2=5 HR.
AVG speed=100/5=20 mph
D

The Q doesn't seem to be from proper GMAT resource as GMAT always has answer choices in order..
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Re: On a journey across Dhaka, a bus averages 10 miles/h for 20% of the  [#permalink]

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New post 19 Dec 2018, 20:01
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Re: On a journey across Dhaka, a bus averages 10 miles/h for 20% of the   [#permalink] 19 Dec 2018, 20:01
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