carroleo wrote:The time it took car A to travel 400 miles was 2 hrs less than the time it took car B to travel the same distance. If Car A's average speed was 10 miles per hour greater than that of car B, what was car B's average speed, in miles per hour?
Can someone please help me solve this and advice on approaches to these speed/distance/time formulas... I cant get my head around them!! Thanks
First, the rate formula:
rate * time = distance, which means time = distance/rate. (We usually just write t = d/r.)
The easiest approach would be to backsolve (plug in the answers).
The answer choices represent the rate of car B. The correct answer likely will be a factor of 400 (the distance). One of the answer choices would say that car B's rate was 40 mph.
If car's B's rate was 40mph, then time for car B would be t = 400/40 = 10.
Car A traveled 10 mph faster. So the rate for car A would be 40 + 10 = 50. The time for car A would be t = 400/50 = 8.
Since the difference in time is 10 - 8 = 2, we would have found the correct answer.
The rate for car B is 40.
Plugging in the answer choices makes the problem much easier to solve. Since the GMAT is a multiple choice test, you should always include the answer choices when you post a question. A question without answer choices is not reflective of an actual GMAT problem.
Hope this helps!
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