Question

A motor car starts with a speed of 70 km/hr with its speed increasing every two hours by 10 km/hr In how many hours will it cover 345 kms?

• A. $2\frac{1}{4}$ hrs
• B. 4 hrs 5 min
• C. $4\frac{1}{2}$ hrs
• D. 3 hrs

Answer 1

Answer: (C)

$4\frac{1}{2}$ hrs

Distance covered in the first 2 hours = (70 x 2) km = 140 km
Distance covered in the next 2 hours = (80 x 2) km = 160 km
Remaining distance = 345 - (140 + 160) = 45 km Now, speed in the fifth hour = 90 km/hr
$\therefore$ Time taken to cover 45 km = $\left(\frac{45}{90}\right)hr=\frac{1}{2}hr$
$\therefore$ Total time taken = $(2+2+\frac{1}{2})hr=4\frac{1}{2}hrs$