Lap race: 600 m track, 220 and 180 m/min

On a 600 m circular track, two runners start together from the same point and run in the same direction at 220 m/min and 180 m/min. After how many minutes does the faster runner first catch up with the slower one?

Step-by-step

1. 220 − 180 = 40
   Moving the same way, the relative speed is the difference of the speeds
2. 600 ÷ 40 = 15
   Catch-up time = distance ÷ relative speed

Why it works

Running the same way round, the faster runner gains one full lap on the slower one before catching up; the gain each minute is the speed difference, so the time is the lap length divided by that difference.

Common mistakes

• Adding the two speeds instead of subtracting them.
• Dividing the 600 m lap by the 220 m/min speed alone.

Related

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