A 5 km racing track is used by two cars. The first car moves at 50 km/h and the second at 80 km/h. If the race starts at 9:00 a.m., at what time will both cars be back at the starting point together?
- 9:10 a.m.
- 9:15 a.m.
- 9:20 a.m.
- 9:30 a.m.
Explanation
Step 1: Time taken for one lap
First car:
5/50=1/10 hour=6 minutes
Second car:
5/80=1/16 hour=3.75 minutes
Step 2: Find when they meet at the starting point together
We need the LCM of 6 minutes and 3.75 minutes.
Convert to seconds:
• 6 minutes = 360 seconds
• 3.75 minutes = 225 seconds
LCM (360, 225) = 1800 seconds = 30 minutes
So, both cars will return to the starting point together after 30 minutes.
Step 3: Add to starting time
9:00 a.m. + 30 minutes = 9:30 a.m.
*
Last updated by NS on 06-09-2026
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