From places A and B, which are 50 km apart, T covers half of the distance in 20 minutes. What should be his speed (in km/h) in the second half so that his average speed from A to B is 80 km/h?
Show answer & explanation
Correct answer: A
Explanation
The Correct answer is option 1 i.e. 85.7
Given that
The total distance from A to B is 50km
the half-distance (25 km) is covered in 20 minutes, i.e. 1/3 hour.
Let the next half distance (25km) be covered with S Km/h speed
The average speed = 80 km/h
Formula used
Average speed = Total distance/total time
Calculation
⇒ 80 = 50/(1/3 + 25/S)
⇒ 5/8 = 1/3 + 25/S
⇒ 25/S = 5/8 - 1/3 = 7/24
⇒ S = 600/7 = 85.72 km/h