A car travels from city A to city B with a constant speed. If the speed of the…
2026
A car travels from city A to city B with a constant speed. If the speed of the car is increased by 20 km/h it will reach destination 1 hour earlier. On the other hand, if its speed decreases by 20 km/h, it reaches 2 hours later than scheduled time. What is the usual time if it travels with routine speed?
- A.
2 hr
- B.
4 hr
- C.
8 hr
- D.
10 hr
Attempted by 10 students.
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Correct answer: B
Let the usual speed be v km/h and usual time be t hours. Distance d = vt.
Case 1: (v + 20)(t - 1) = vt ⇒ vt - v + 20t - 20 = vt ⇒ v = 20t - 20.
Case 2: (v - 20)(t + 2) = vt ⇒ vt + 2v - 20t - 40 = vt ⇒ v = 10t + 20.
Equating expressions for v: 20t - 20 = 10t + 20 ⇒ 10t = 40 ⇒ t = 4 hours.