A, B and C run around a circular track starting from the same point simultaneously and in the same direction at speeds of 4 kmph, 6 kmph and 8 kmph respectively. If the length of the track is 400 meters, when will A, B and C meet at the starting point for the first time after they started the race?
Well, I used backsolving and elimination for time consideration,
Since among ABC, A is the slowest runner, it will take at least
0,4/4 = 6 mins, so eliminate A and B
Start backsolving with C, 12 min=1/5 hours.
Multiply ABC speeds by the time, 1/5 hours, if the results are all multiples of 0,4 they do meet after this time at the starting point.
And since 12 min is the smallest value among left choices it must be the shortest time.