Multiple choice

Sangram goes to his office by car at the speed of 40 Km/h and reaches 30 minute earlier. If he goes at the speed of 30 Km/h, he reaches 30 minutes late. What will be the speed (in Km/hr) of the car to reach on time?

  1. $\(\frac{120}{7}\)$
  2. $\(\frac{240}{7}\)$
  3. $\(\frac{360}{7}\)$
  4. $\(\frac{60}{7}\)$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let distance be D km and on-time speed be S km/h. At 40 km/h, reaches 30 min early: D/40 = T - 0.5. At 30 km/h, reaches 30 min late: D/30 = T + 0.5. Subtracting gives D/30 - D/40 = 1, so D(1/30 - 1/40) = 1, D(4/120 - 3/120) = 1, D(1/120) = 1, so D = 120 km. Then T = 120/40 + 0.5 = 3.5 hours. Speed to be on time = 120/3.5 = 240/7 ≈ 34.29 km/h.

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