SOLUTION: Cory and Melissa are racing electronic cars around a circular track. They begin at the same time going in the same direction. Cory's car completes a revolution in 40 seconds, while

Question 266643: Cory and Melissa are racing electronic cars around a circular track. They begin at the same time going in the same direction. Cory's car completes a revolution in 40 seconds, while Melissa's car completes a revolution in 35 seconds. How long will it take them before both cars reach the starting point again simultaneously?

Answer by ptaylor(2198) (Show Source): You can put this solution on YOUR website!
OK. We need to find the lowest number that is divisible by both 40 and 35---in other words, the Least Common Multiple (LCM)
Here's one way to do that(reduce each to prime numbers):
40=2*20=2*5*4=2*5*2*2
35=7*5
Since both contain 5, we need only to use 5 once.
so, we have 7*5*2*2*2=280 sec
In 280 sec, Cory's car completes exactly 8 revolutions
In 280 sec, Melissa's car completes exactly 7 revolutions
Therefore, after 280 sec, they have both returned to the starting point at the same time.
Hope this helps--ptaylor
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