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A motorbike leaves point AA at 11 pm and moves towards point BB at a uniform speed. A car leaves point BB at 22 pm and moves towards point AA at a uniform speed which is double that of the motorbike. They meet at 3:403:40 pm at a point which is 168 km168 \mathrm{~km} away from AA . What is the distance, in km, between AA and BB ?

Solution

✅ Correct Option: 2

We first map out what happens when:

1:00 PM: Motorbike leaves point A

2:00 PM: Car leaves point B

3:40 PM: They meet at a point 168 km from A


Motorbike's travel time: From 1:00 PM to 3:40 PM

3:40 PM - 1:00 PM = 2 hours 40 minutes = 223\tfrac{2}{3} hours = 83\tfrac{8}{3} hours

Car's travel time: From 2:00 PM to 3:40 PM

3:40 PM - 2:00 PM = 1 hour 40 minutes = 123\tfrac{2}{3} hours = 53\tfrac{5}{3} hours


We know the motorbike traveled 168 km in 83\tfrac{8}{3} hours.

Using Speed = Distance ÷ Time:

Motorbike's speed = 168÷83168 \div \tfrac{8}{3}

=168×38= 168 \times \tfrac{3}{8}

=63= 63 km/h


The problem states the car's speed is double that of the motorbike.

Car's speed = 2×63=1262 \times 63 = 126 km/h


The car traveled for 53\tfrac{5}{3} hours at 126 km/h.

Distance traveled by car = 126×53=210126 \times \tfrac{5}{3} = 210 km


Since they meet at a point between A and B:

Distance from A to meeting point = 168 km

Distance from B to meeting point = 210 km

Total distance between A and B = 168+210=378168 + 210 = 378 km


When two objects move towards each other and meet, the total distance they cover together equals the distance between their starting points. This is a fundamental concept in relative motion problems that will help you solve similar questions quickly!

Answer: 378 km

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