Question

a boy travels with a speed of 30kmph for first 1/3 journey time. during the remaining journey time he travels with a speed V kmph so that average speed of the boy is 40kmph, then find V.
answer is 45kmph
want the solution​

Answer 1

a boy travels with a speed of 30 kmph for first 1/3 journey time during the remaining journey time he travels with a speed 60kmph find the average speed of the boy

:

Let t = total time

then

1%2F3t = time at 30 km/h

and

2%2F3t = time at 60 km/h

:

Let a = average speed for the journey

:

Write a distance equation: dist = speed * time

:

30km/h dist + 60 km/h dist = total dist

30*1%2F3t + 60*2%2F3t = at

We can cancel out the denominators

10t + 20(2t) = at

10t + 40t = at

we don't care about t, divide thru by t and eliminate it

10 + 40 = a

a = 50 km/h is the average speed