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
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.
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