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

Distance covered in first 2 hours :
= (70 × 2) km
= 140 km
Distance covered in next 2 hours :
= (80 × 2) km
= 160 km
Remaining distance :
= 345 - (140 + 160)
= 45 km
Speed in the fifth hour = 90 km/hr
Time taken to cover 45 km :
= $$\frac{45}{90}$$ hr
= $$\frac{1}{2}$$ hr
∴ Total time taken :
= 2 + 2 + $$\frac{1}{2}$$
= $$4\frac{1}{2}$$ hrs