A car starts with the speed of 70 km/hr with its speed increasing every two hours by 10 km/hr. In how many hours will it cover 345 kilometers?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 4.5 hrs
The speed is fixed within each two-hour block and rises by 10 km/h at the start of the next block, so add the distance block by block until 345 km is reached.
Hours 1–2 at 70 km/h: \(2\times70=140\) km (total 140 km)
Hours 3–4 at 80 km/h: \(2\times80=160\) km (total 300 km)
Left to cover: \(345-300=45\) km at 90 km/h
Time for it \(=\displaystyle\frac{45}{90}=0.5\) h
Total time \(=4+0.5=\) 4.5 hours.