vishal.pathak wrote:A car traveling at a certain constant speed takes 2 seconds longer to travel 1 kilometer than it would take to travel 1 kilometer at 75 kilometers per hour. At what speed, in kilometers per hour, is the car traveling?
A. 71.5 B. 72 C. 72.5 D. 73 E. 73.5
What is the fastest way of solving this problem
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 time and rate have a reciprocal relationship, 25/24 of the normal time implies 24/25 of the normal rate:
(24/25)*75 = 72.
The correct answer is
B.
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