UGC NET Questions (Paper – 1)

Average speed is defined as total distance divided by total time, not the average of the two speeds. The car travels 120 km each way, so the total distance is 240 km. The time taken in the first leg is 120 ÷ 40 = 3 hours and in the return leg is 120 ÷ 60 = 2 hours, giving a total of 5 hours. Dividing 240 by 5 yields 48 km/h as the average speed for the entire journey.

Option A:
Option A, 45 km/h, might be guessed by taking a simple average of the two speeds or by an approximate calculation, but it does not correspond to the correct total distance over total time.

Option B:
Option B uses the exact definition of average speed and calculates both distances and times explicitly. It also matches the harmonic mean formula for a round trip with equal distances, which simplifies to 2ab/(a + b).

Option C:
Option C, 50 km/h, exceeds the true average because more time is spent at the lower speed, pulling the overall average below the midpoint between 40 and 60.

Option D:
Option D, 52 km/h, is even higher and clearly inconsistent with spending a substantial part of the journey at just 40 km/h.