Two cars 360 km apart: when do they meet?

Two cars start 360 km apart and drive toward each other at 80 km/h and 40 km/h. How long until they meet?

Step-by-step

1. 80 + 40 = 120
   Moving toward each other, the relative speed is the sum of the speeds
2. 360 ÷ 120 = 3
   Time to meet head-on = distance ÷ relative speed

Why it works

Driving toward each other, the two cars close the gap at the sum of their speeds, so the meeting time is the total distance divided by that sum.

Common mistakes

• Subtracting the speeds instead of adding them.
• Dividing 360 km by only one car's speed.

Related

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