A man drives from Mzumbe to Kibaha,a distance of 48km in 45min. Where the surface is good he drives at 72km/h, where the surface is bad he drives at 48km/h. Find the number of kms of good surface.
From the definition of you get
Now you can set up an equation in x:
(Keep in mind that the speed is given in kilometers per hour and the elapsed time in minutes, which have to be changed to hours too!)
Solve the equation above for x. I've got x = 36 km. Consequently the bad road is 12 km long.