Question 951519
two runners run around a circular track. the first runner completes a lap in 7 minutes. the second runner completes a lap in 13 minutes. If they both start at the same place and same time and go in the same direction, after how many minutes will they meet again at the starting place?
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let x=number of minutes after which both runners meet at the stating place
x/7=13
or 
x/13=7
x=7*13=91
after 91 minutes , faster runner completes 13 laps, and slower runner completes 7 laps, both runners meeting at the starting place.