From home to school, he travels at
5 km/h.

So to travel every 1 km, he would need 1/5 h.

From school to home, he travels at 4 km/h.

So to travel every 1 km, he would need 1/4 h.


Let's compare the the ratio of the time he takes to travel every 1 km

1/5 : 1/4

= 1 : 5/4

= 4 : 5

The distance from school to home and from home to school is the same.

So you can treat this as 4 units of time are needed to travel from home to school, and 5 units of time to travel from school to home.

Total = 4 + 5 = 9 units

Now, we know total time taken is 45 min.


So , 45 min = 9 units.

1 unit = 45 min ÷ 9 = 5 min


So, time taken to travel from home to school

= 4 units
= 4 x 5 min
= 20 min

Another way to see the ratio of time needed to travel 1 km :

1/4 h = 15/60 h = 15 min

1/5 h = 12/60 h = 12 min

Ratio of time (home to school) : (school to home)

= 12 min : 15 min
= 4 : 5