A train takes two hours to travel from one station to the other.

Question

A train takes two hours to travel from one station to the other. What is the distance between the two stations?

(1) The train covers one-third of the total distance in the first hour at an average speed of 80 mph.

(2) The average speed during the second hour is 160 mph.

chetan2u · Answer

A train takes two hours to travel from one station to the other. What is the distance between the two stations?

(1) The train covers one-third of the total distance in the first hour at an average speed of 80 mph.
So 1/3rd of total is covered in 1 HR at 80mph...
At 80mph, train will cover 80miles in 1 HR and this is 1/3rd of total
So total =80*3=240miles
Sufficient

(2) The average speed during the second hour is 160 mph.
We do not know what proportion is this distance..
Insufficient

A

delta23 · Answer

chetan2u

Can I assume the speed is constant throughout the journey? Then yes, statement 1 alone is sufficient.

chetan2u · Answer

No the speed need not be constant..
It is given that it travels 1/3 rd distance in 1 HR traveling at an average speed of 80mph..
So 1st HR average speed 80mph, so he traveled 80 miles in that 1 hour.
But now this 80 miles are given as 1/3rd distance, so totalis 1/3+1/3+1/3= 80+80+80=240
Average speed in 2nd HR will be different as it is covering 2/3rd distance in 1 hr

KarishmaB · Answer

Responding to a pm:

Here is the thing about average speed - it is not constant speed. 
If my average speed is 50 mph for an hour, all I can say is that I took 1 hour to cover 50 miles of distance. At what speed I actually drove, I cannot say. For some mins, I could have driven at 20 mph, for some I could have driven at 80 mph and so on. Overall, whatever I did, it led to me covering 50 miles in 1 hour.

(1) The train covers one-third of the total distance in the first hour at an average speed of 80 mph.
The average speed of the train was 80 mph. This means the train covered 80 miles in the first hour - that is all the information I get. At what speed did the train actually run at different times, we cannot say.
We are also given that it covers 1/3rd of the distance in this one hour. So 80 miles is 1/3rd of the total distance. 
Hence total distance must be 240 miles. This is what we were asked. 
Hence, sufficient.

(2) The average speed during the second hour is 160 mph.
This tells us that the train covered 160 miles in the second hour. But without using data from stmnt 1, we cannot say how much distance it covered in the first hour. Hence this statement alone is not sufficient.

Answer (A)

delta23 · Answer

KarishmaB ,

Just because they had given a hint in statement 1 stating 1/3 of the journey was covered, we were able to arrive at the total distance. Am I missing here something?

KarishmaB · Answer

You are correct. Since you are given that it was 1/3rd of the total distance, you can find the total distance using stmnt 1 alone.

Archit3110 · Answer

target find distance b/w 2 stations
#1
The train covers one-third of the total distance in the first hour at an average speed of 80 mph.
x/3 = 80*1
x = 240
240 sufficient
#2
The average speed during the second hour is 160 mph
insufficient
as distance covered is not known
option A

A train takes two hours to travel from one station to the other.

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A train takes two hours to travel from one station to the other.

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