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09 Apr 2020, 03:58
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D
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
65%
(hard)
Question Stats:
68% (03:26) correct
32%
(03:03)
wrong
based on 210
sessions
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Not Attempted Yet
John runs on a circular track A at 6 kmph and Mary runs on a circular track B at 7.5 kmph. The total length of tracks A and B is 325 metres. John covers 9 rounds on track A in the same time as Mary covers 5 rounds on track B. How many seconds does Mary need to make one round on track A?
A. 42
B. 44
C. 46
D. 48
E. 50
Are You Up For the Challenge: 700 Level Questions
A. 42
B. 44
C. 46
D. 48
E. 50
Are You Up For the Challenge: 700 Level Questions
Updated on: 09 Apr 2020, 04:43
Originally posted by DeusTacitus22 on 09 Apr 2020, 04:26.
Last edited by DeusTacitus22 on 09 Apr 2020, 04:43, edited 1 time in total.
Last edited by DeusTacitus22 on 09 Apr 2020, 04:43, edited 1 time in total.
Kudos
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John = 6kmph = 5/3mps
Mary = 7.5kmph = 25/12mps
We know, A+B=325m
Acc. to Question,
=> (9A)*3/5 = (5B)*12/25
=> 9A = 4B => B = 9A/4
Substituting in above eqn.
=> A = 100m
Total time taken by Mary
=> 100*12/25 => 48 sec
The Answer - D
Mary = 7.5kmph = 25/12mps
We know, A+B=325m
Acc. to Question,
=> (9A)*3/5 = (5B)*12/25
=> 9A = 4B => B = 9A/4
Substituting in above eqn.
=> A = 100m
Total time taken by Mary
=> 100*12/25 => 48 sec
The Answer - D
General Discussion
09 Apr 2020, 04:31
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The total length of tracks A and B is 325m, hence A+B=0.325km ----(1)
John covers 9 rounds of track A in the same time that Mary covers 5 rounds on track B.
Hence \(\frac{9A}{6}=\frac{5B}{7.5}\)
\(9*7.5A=30B\)
\(B=2.5A\)
Substitute \(B=2.5A\) into (1)
\(3.25A=0.325\)
\(A=0.1km\)
Time taken by Mary in seconds to make 1 round on track A \(= \frac{0.1}{7.5}*3600 = \frac{3600}{75} = 12*4 = 48 sec.\)
The answer is D.
John covers 9 rounds of track A in the same time that Mary covers 5 rounds on track B.
Hence \(\frac{9A}{6}=\frac{5B}{7.5}\)
\(9*7.5A=30B\)
\(B=2.5A\)
Substitute \(B=2.5A\) into (1)
\(3.25A=0.325\)
\(A=0.1km\)
Time taken by Mary in seconds to make 1 round on track A \(= \frac{0.1}{7.5}*3600 = \frac{3600}{75} = 12*4 = 48 sec.\)
The answer is D.
