A car travels for 11 hours. For the first 100 km, the car travels with a certain speed, and then it increases its speed by 15 km/h to cover the remaining 280 km. The time (in hours) it takes to travel the 100 km part is:
Show answer & explanation
Correct answer: A
Explanation
The correct answer is Option 1 i.e. 4.
Let speed = x → time for 100 km = 100/x
Next speed = x + 15 → time for 280 km = 280/(x + 15)
Total time = 11 ⇒ 100/x + 280/(x + 15) = 11
Solve:
Multiply and simplify → 11x² − 215x − 1500 = 0
Factors: (11x + 60)(x − 25) = 0 ⇒ x = 25
Time = 100/25 = 4 hours