Multiple choice

Rahul starts travelling at the speed of 50 kmph from A to B, 180 km apart. The speed of Rahul decreases by 10% every hour. What is the total time taken by Rahul to go from A to B?

  1. 4.25 h

  2. 5.15 h

  3. 5.75 h

  4. 6.15 h

  5. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Rahul travels 50 km in the first hour, 45 km in the second, 40.5 km in the third, and 36.45 km in the fourth. Total distance covered in 4 hours is 171.95 km. The remaining 8.05 km is covered at a speed of 32.805 km/h, taking approximately 0.245 hours, totaling 4.245 hours.

AI explanation

The total distance is 180 km. Using the formula for the sum of a geometric progression, the distances covered each hour form a series where the first term is 50 and the common ratio is 0.9. The total distance covered in 4 hours is 50 multiplied by the sum of (0.9 raised to the power of 0, 1, 2, and 3), which equals 50 times 3.439, resulting in 171.95 km. The remaining distance is 8.05 km, which is covered in the fifth hour at a speed of 32.805 km/hr, taking 0.245 hours. The total time taken is 4 + 0.245, which equals 4.25 h.

Keep practicing — related questions