Multiple choice

If a car travels a distance with 20% less speed, then it will reach 15 minutes late. What is the usual time (in minutes) taken by the car to travel the same distance?

  1. 80

  2. 90

  3. 75

  4. 60
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let the usual speed be v and usual time be t. New speed is 0.8v. Since distance is constant, v * t = 0.8v * (t + 15). Dividing by v, t = 0.8t + 12. Thus, 0.2t = 12, so t = 60 minutes.

AI explanation

When speed decreases by 20%, the new speed becomes 80% of the original speed, making the speed ratio of usual to new equal to 5:4. Because time is inversely proportional to speed for a constant distance, the time ratio becomes 4:5. The difference of one unit equals the 15 minutes of delay, meaning four units equals 60 minutes. The usual time taken by the car is 60 minutes.

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