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2 seconds longer per 1k = 150 seconds longer per 75k.Needgmat wrote:A car travelling at a certain constant speed takes 2 second longer to travel 1 kilometer that it would take to travel 1 kilometer at 75 kilometer per hours. At what speed in kilometers per hour, is the car traveling?
A) 71.5
B) 72
C) 72.5
D) 73
E) 73.5
Hi GMATGuruNY ,2 seconds longer per 1k = 150 seconds longer per 75k.
Since there are 3600 seconds in 1 hour, the additional time needed to travel 75k at the slower rate = 150/3600 = 1/24 hours.
Since the slower time is 1/24 longer than the faster time, the slower time is 25/24 of the faster time.
Time and rate are RECIPROCALS.
Since the slower time is 25/24 of the faster time, the slower rate is 24/25 of the faster rate:
(24/25)(75) = 72.
The correct answer is B.
Alternate approach:Needgmat wrote:A car travelling at a certain constant speed takes 2 second longer to travel 1 kilometer that it would take to travel 1 kilometer at 75 kilometer per hours. At what speed in kilometers per hour, is the car traveling?
A) 71.5
B) 72
C) 72.5
D) 73
E) 73.5
Needgmat wrote:A car travelling at a certain constant speed takes 2 second longer to travel 1 kilometer that it would take to travel 1 kilometer at 75 kilometer per hours. At what speed in kilometers per hour, is the car traveling?
A) 71.5
B) 72
C) 72.5
D) 73
E) 73.5
OAB
Please explain.
Many thanks in advance.
Kavin
Hi GMATGuruNY ,Alternate approach:
(75 kilometers)/(1 hour) = (75 kilometers)/(3600 seconds) = (1 kilometer)/(3600/75 seconds) = (1 kilometer)/(48 seconds).
Since the car takes 2 seconds longer to travel 1 kilometer, the rate = (1 kilometer)/(50 seconds).
(1 kilometer)/(50 seconds) * (3600 seconds)/(1 hour) = 72 kilometers per hour.
The correct answer is B.
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