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It took the bus 4 hours to get from town A to town B. What

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It took the bus 4 hours to get from town A to town B. What [#permalink] New post 02 Aug 2008, 02:45
It took the bus 4 hours to get from town A to town B. What was the average speed of the bus for the trip?

1.In the first 2 hours the bus covered 100 miles
2.The average speed of the bus for the first half of the distance was twice its speed for the second half
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Re: DATA INSUFF.. [#permalink] New post 02 Aug 2008, 06:57
arjtryarjtry wrote:
It took the bus 4 hours to get from town A to town B. What was the average speed of the bus for the trip?

1.In the first 2 hours the bus covered 100 miles
2.The average speed of the bus for the first half of the distance was twice its speed for the second half


average speed = total distance / total time = d/4

so we have to find out d

statement 1 : we dont know the distance the bus covered in second two hours.. not suff
statement 2 : d/(2t1) = 2d/(2t2)
t2 = 2t1
we know t1+t2 = 4
so t1 = 4/3
and t2 = 8/3
still we cant find d ... so not suff

combine two statements

distance covered in 2 hours = distance covered in t1 (4/3) hours + distance covered in (2-4/3) hours
100 = d/2 + d/(2t2) * (2-4/3)
100 = d/2 + 3d/(2*8) * ((6-4)/3)
100 = d/2 + d/8

suff... actually no need to solve it. we know we can find d and the average speed.... Option C
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Re: DATA INSUFF.. [#permalink] New post 02 Aug 2008, 10:33
durgesh79 wrote:
arjtryarjtry wrote:
It took the bus 4 hours to get from town A to town B. What was the average speed of the bus for the trip?

1.In the first 2 hours the bus covered 100 miles
2.The average speed of the bus for the first half of the distance was twice its speed for the second half


average speed = total distance / total time = d/4

so we have to find out d

statement 1 : we dont know the distance the bus covered in second two hours.. not suff
statement 2 : d/(2t1) = 2d/(2t2)
t2 = 2t1
we know t1+t2 = 4
so t1 = 4/3
and t2 = 8/3
still we cant find d ... so not suff

combine two statements

distance covered in 2 hours = distance covered in t1 (4/3) hours + distance covered in (2-4/3) hours
100 = d/2 + d/(2t2) * (2-4/3)
100 = d/2 + 3d/(2*8) * ((6-4)/3)
100 = d/2 + d/8

suff... actually no need to solve it. we know we can find d and the average speed.... Option C



i didnt get the simplification part.. kindly explain
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Re: DATA INSUFF.. [#permalink] New post 02 Aug 2008, 10:49
arjtryarjtry wrote:
durgesh79 wrote:
arjtryarjtry wrote:
It took the bus 4 hours to get from town A to town B. What was the average speed of the bus for the trip?

1.In the first 2 hours the bus covered 100 miles
2.The average speed of the bus for the first half of the distance was twice its speed for the second half


average speed = total distance / total time = d/4

so we have to find out d

statement 1 : we dont know the distance the bus covered in second two hours.. not suff
statement 2 : d/(2t1) = 2d/(2t2)
t2 = 2t1
we know t1+t2 = 4
so t1 = 4/3
and t2 = 8/3
still we cant find d ... so not suff

combine two statements

distance covered in 2 hours = distance covered in t1 (4/3) hours + distance covered in (2-4/3) hours
100 = d/2 + d/(2t2) * (2-4/3)
100 = d/2 + 3d/(2*8) * ((6-4)/3)
100 = d/2 + d/8

suff... actually no need to solve it. we know we can find d and the average speed.... Option C



i didnt get the simplification part.. kindly explain


distance covered in first 2 hours = 100 (as per statement 1)
distance covered in first 4/3 hours = d/2 (as per statement 2)
distance covered in first (2-4/3) hours = average speed during this journey * time
= 3d / (2*8) * (2 - 4/3) ------> we know that for second half of the journey the time taken is 8/3 from statement 2
= d/8

so 100 = d/2 + d/8
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Re: DATA INSUFF.. [#permalink] New post 05 Aug 2008, 02:08
EDIT : Just found this question in GMAT club tests.. and now i'd like to correct myself
the right answer is E
Re: DATA INSUFF..   [#permalink] 05 Aug 2008, 02:08
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