Correct option is (b) 40 km/hr
Train was halted for half an hour.
So, total time taken in Journey = 23 - (\(\frac 12\)) = 22.5 hours.
Average speed in Whole Journey = \(\frac {1000}{22.5}\) = 44.5 km/hr.
The average speed on return journey is 20% less than onward journey.
Therefore, ratio of average speed of onward and return journey,
= \(\frac{100}{80}\)
= \(\frac 54\)
Let average speed of onward journey = 5x.
Average speed on return journey = 4x.
Average speed on whole journey = \(\frac{(5x + 4x)}2\)
44.5 = \(\frac{(5x + 4x)}2\)
89 = 9x
x = 9.88.
Average speed on return = 9.88 x 4
= 39.52
= 40 kmph (Approx.)
