# Help with problem

• Dec 8th 2008, 01:16 AM
MTAALAMU
Help with problem
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.
• Dec 8th 2008, 03:33 AM
earboth
Quote:

Originally Posted by MTAALAMU
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.

Let x denote the number of kilometers of the road in good condition. Then (48 - x) is the number of kilometers of the road in bad condition.

From the definition of \$\displaystyle speed = \dfrac{distance}{time}\$ you get \$\displaystyle time = \dfrac{distance}{speed}\$

Now you can set up an equation in x:

\$\displaystyle \dfrac x{72} + \dfrac{48-x}{48}=\dfrac{45}{60}\$

(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.