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bus trip

by blaster » Wed Jun 29, 2011 8:38 pm
if it took a bus three hours to get from town A to B ,what was the average speed of the bus for the entire trip?

1) During the first hour the bus finished 1/3 of the distance going 60 kmh.
2) During the second hour the average speed of the bus was 120 kmh, twice it's speed during third hour.
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Source: — Data Sufficiency |
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by blaster » Wed Jun 29, 2011 8:39 pm
OA is A. But i don't agree. pls explain
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by Frankenstein » Thu Jun 30, 2011 12:47 am
Hi,
Avg speed = Total Distance(d)/Total time taken(t)
Given that t = 3 hours
From(1):
In 1 hour it traveled at 60km/hr.
So, distance in 1 hour is 1*60 = 60km
This is 1/3 of total distance.
So, d/3 = 60 =>d = 180
Given t=3 hrs.
So, avg sped = 180/3 = 60km/hr
Sufficient
From(2):
We can calculate distance traveled by the bus from 1 hour to 3 hours. But, we do not know the distance traveled by bus n the first hour
Not sufficient

Hence, A
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by blaster » Thu Jun 30, 2011 2:12 am
what i don't understand is why you assume that other 2/3 part of the road is also gone in 60 kmh (each 1/3)?
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by Frankenstein » Thu Jun 30, 2011 2:32 am
blaster wrote:what i don't understand is why you assume that other 2/3 part of the road is also gone in 60 kmh (each 1/3)?
Hi,
I didn't make any assumption. I have calculated the distance for the first 1 hour as we know the speed for 1st hour.
This distance is given as 1/3 of total distance in statement(1). So, total distance will be 3 times the calculated distance.
In the premise, it is given it takes 3 hours. So, to calculate avg. speed, I just divided the total distance with total time(3 hours).
if it took a bus three hours to get from town A to B ,what was the average speed of the bus for the entire trip?
1) During the first hour the bus finished 1/3 of the distance going 60 kmh.
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by amit2k9 » Thu Jun 30, 2011 10:38 pm
a 60 = 1/3 * total distance
thus total distance = 180. total time = 3 hrs hence average speed = 60km/hr. sufficient,

b no mention about the distance in 1st hour.not sufficient.

A it is.
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by goalevan » Sun Jul 03, 2011 4:13 pm
I agree with answer choice A, and that statement 2 is insufficient, but doesn't it contradict statement 1?

Statement 1 says that for 1 hour, the bus travels at 60km/hr. 1hr * 60km/hr = 60km. It says that this is 1/3 of the total distance traveled. 60km * 3 = 180km total distance.

Statement 2 says that for the second hour, the bus travels at 120km/hr. 1 hr * 120km/hr = 120km. It also says that it travels at half that speed for the third hour. 1 hr * 120/2 km/hr = 60km.

Distance from hour 2 + distance for hour 3 = 180km, the same distance that the first statement says is equal to the total distance, which would make the distance traveled in the first hour 0km/hr.

Data sufficiency statements should never give differing information. What am I missing here?
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