A boy has to cover 4km to caught he walk part of the distance at 3km/h rans the rest at 5 km/h if takes 1hour to complete the distance for how many km does he walk?
Let's assume that the boy walks for x km and runs for (4-x) km.
The time taken to walk x km at 3 km/h is given by: time = distance/speed = x/3
The time taken to run (4-x) km at 5 km/h is given by: time = distance/speed = (4-x)/5
According to the problem, the total time taken to cover the distance is 1 hour. Therefore, we can write:
x/3 + (4-x)/5 = 1
Multiplying both sides by 15, we get:
5x + 3(4-x) = 15
Simplifying the equation, we get:
5x + 12 - 3x = 15
2x = 3
x = 1.5 km
Therefore, the boy walks for 1.5 km and runs for (4-1.5) = 2.5 km.