Question

A motor starts with the speed of 70 kmph with its speed increasing every two hours by 19 kmph. In how many hours will it cover 345 kms?

Options

• `2 1/4` hours

• `4 1/2` hours

• 4 hours 5 minutes

• Cannot be determined

Answer 1

`4 1/2` hours

Explanation: = / = 

Initial speed of motor = 70 kmph

Distance covered in first 2 hours = 2 × 70 = 140 kms

For next two hours speed of motor = 80 kmph

∴ Distance covered in next 2 hours = 2 × 80 = 160 kms

Distance covered in first 4 hours = 140 + 160 = 300

Remaining distance = 345 – 300 = 45 km

This distance will be covered at the speed of 90 kmph

∴ Time taken = `45/90 = 1/2` hour

∴ Total time = `4 + 1/2 = 4 1/2` hours