Two buses start from the same station at 9.00am and travel in opposite directions along the same straight…

Analyze the question: Two buses leave the same point at the same time and move in opposite directions. The distance between them grows at the sum of their speeds. We need the time at which that distance reaches 240 km.

Concept: When two objects move in opposite directions, the relative speed is the sum of their speeds:

Relative speed = 72 + 48 = 120 km/h

Time = Distance ÷ Speed

Solution:

Time = 240 ÷ 120 = 2 hours

Start time = 9:00 am

Time they are 240 km apart = 9:00 am + 2 hours = 11:00 am

Check:

• First bus: 72 × 2 = 144 km
• Second bus: 48 × 2 = 96 km
• Total: 144 + 96 = 240 km ✓

Tip: For "opposite directions" questions, add the speeds. For "same direction" questions, subtract them. Then use Time = Distance ÷ Speed, and remember to add the time to the starting clock time.