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06 Jun 2019, 18:43
Kudos
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B
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Difficulty:
35%
(medium)
Question Stats:
77% (02:37) correct
23%
(03:12)
wrong
based on 137
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Adam, Bob, and Carol started from the same place and traveled in the same direction at a speed of 30 miles/hour, 40 miles/hour and 60 miles/hour respectively. Bob started two hours after Adam. If Bob and Carol overtake Arun at the same instant, how many hours after Adam did Carol start?
A. 2 hours
B. 4 hours
C. 7 hours
D. 10 hours
E. 14 hours
A. 2 hours
B. 4 hours
C. 7 hours
D. 10 hours
E. 14 hours
06 Jun 2019, 19:35
Kudos
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Relative distance between A and B just before B starts- 2*30=60
Relative speed of B wrt A= 40-30=10
Time taken by B to overtake A= 60/10=6 hrs
Hence C will overtake A after A has traveled for= (6+2)=8 hrs
Total distance C will travel to overtake A= 30*8=240
Time taken by C to travel 240 Kms= 240/60=4 hrs
Number of hours after A did C start= 8-4=4hrs
Relative speed of B wrt A= 40-30=10
Time taken by B to overtake A= 60/10=6 hrs
Hence C will overtake A after A has traveled for= (6+2)=8 hrs
Total distance C will travel to overtake A= 30*8=240
Time taken by C to travel 240 Kms= 240/60=4 hrs
Number of hours after A did C start= 8-4=4hrs
DisciplinedPrep
06 Jun 2019, 20:33
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DisciplinedPrep
Adam and Bob
After two hours Adam is 30*2=60 miles ahead..
Bob covers 40-30 miles in one hour, so B will cover 60 in 60/10 or 6hours..
Bob and carol
They overtake at the same instant, so distance covered is same..
Straight - speed are in ratio 40:60 or 4:6, so time spent will be 6:4.. B takes 6 hrs, so C takes 4 hrs
Algebraic Method - A covers 30*(6+2) = 240 miles in 6+2 hrs..
So, C covers this distance in \(\frac{240}{60}=4\)hrs
B
