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Doubts of Time and Distance sheet -1

In this forum, please discuss the questions appearing in the QA class sheets :especially the practice and the DS questions at the end of the sheet.

Doubts of Time and Distance sheet -1

Postby sadmin » Tue Feb 26, 2013 9:56 am

Please post your doubts of time and distance sheet 1 on this thread.
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Re: Doubts of Time and Distance sheet -1

Postby gaurav1399 » Fri Mar 01, 2013 5:50 am

I am having problem solving question 15 and 27 of practice questions.
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Re: Doubts of Time and Distance sheet -1

Postby Anantdeep » Fri Mar 01, 2013 5:51 am

Data sufficieny Q4 ; In statement II are we supposed to assume the usual speed as 5km/hr from the 1st statement?? Generally, we do not corelate statements in DS, and they are treated as independent.
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Re: Doubts of Time and Distance sheet -1

Postby sadmin » Fri Mar 01, 2013 5:52 am

15. A certain distance is covered with a certain speed. If 1/3
of the distance is covered in triple time, then the ratio of
the speed to that of the original one is
(a) 9 : 1 (b) 1 : 9 © 3 : 1 (d) 1 : 3

Solution

Let the distance -be 30 km and the speed by 5 kmph - so time = 6 hours
Now one third of the distance is covered in triple the time - therefore the speed = 10/18 =

The ratio of speeds = 5 :10/18 = 9:1 but the question has asked for new speed to the original speed , there fore the answer must be 1:9
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Re: Doubts of Time and Distance sheet -1

Postby sadmin » Fri Mar 01, 2013 5:53 am

Q27. Two guns were fired from the same place at an interval
of 13 minutes but a person in a train approaching the
place hears the second report 12 minutes 30 seconds
after the first. Find the speed of the train in kmph,
supposing that sound travels 330 metres per second.

Solution

Let the guns be located at a point say A and the approaching person hear the first report of the gun at point B and the second report at point C.( You should draw this on a piece of paper to understand this further)

If the person were stationary at point B, i.e. the point where he hears the first report , he would hear the second report exactly after 13 minutes.

But he has moved to point C and he has been moving for 12 minutes and 30 seconds to reach point C from point B. Where as the sound reaches the point B after 13 minutes, i,e, 30 seconds more that the time it takes to reach the point C.

Thus we can conclude that the time taken by the man on the motorcycle to travel from B to C is 12 minutes and 30 seconds while the sound wil take exactly 30 seconds to travel the same distance

Thus we have the equation

SPEED of the man x 12.5 minutes = speed of sound x 0.5 minutes

On solving we can find the speed of the man.

Speed of the man = 330/25 = 13.2 m/s

=> 13.2 x 18/5 = 2.64 x 18 = 47 .something should be the answer
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Re: Doubts of Time and Distance sheet -1

Postby sadmin » Fri Mar 01, 2013 5:53 am

Q4 DS
Find the distance ‘d’ that Ravi covers
I. If he walks at 5 km/hr to reach the destination 7 minutes
late. However, had he walked at 6 km/hr, he
would have reached the destination 8 minutes earlier.
II. Walking 4/5 of his usual speed, he reached the destination
12 minutes late.

Solution
No when considering the second statement alone - do not assume any value that is provided from statement 1. Thus the question can be answered by statement 1 alone but not by statement 2 alone.
Thus answer to this question should be A
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