Question

A car covers the first half of the distance in 40 km/hr and the second half in 60 km/hr. what is the avrage speed of the car?

Answer 1

let a = average speed for the trip
let d = half of the distance

we know time = dist/speed
so for the first half time = d/40
for the 2nd half time = d/60
for the total distance = 2d/a

Hence, d/40 + d/60 = 2d/a
or 1/40 + 1/60 = 2/a
or (3+2)/120 = 2/a
5a = 240
a = 240/5
a = 48 km/hr Ans.