SSC CPO 2024 PYQ — Question 122

The correct answer is option 1 i.e. 75.48.

Given that, distance between A and B = 800 km

Speed of train from a to B = 90 km/h

Speed of train from B to A = 65 km/h

Average speed = Total distance/Total Time

According to the given question,

Time taken by train to go from A to B = $800 \over 90$ = $80 \over 9$ h

Time taken by train to go from B to A = $800 \over 65$ = $160 \over 13$ h

Total time = ${80 \over 9} + {160 \over 13}$

⇒ ${1040 + 1440} \over 117$ = $2480 \over 117$ h

Total distance = 2 × 800 = 1600 km

Average speed = ${1600 \over {2480 \over 117}}$

⇒ $187200 \over 2480$ = 75.48

Hence the average speed(in km/h) of the train during the whole journey is 75.48.