<PRE><B>Question 952789</B>
A boy walks from his house to school at 2.5km/h and arrives 12 minutes late.
The next day he walks at 4km/h and reaches the school 15 minutes earlier.
 So determine the distance between the house and the school. 
:
let d = the distance from the house to the school
Convert min to hrs
12 min = 12/60 = .2 hrs late
15 min = 15/60 = .25 hrs early
The time difference between the two trips is .45 hrs
:
2.5 km/h time - 4 km/h time = .45 hrs
{{{d/2.5}}} - {{{d/4}}} = .45
multiply by 20 to clear the denominators
20*{{{d/2.5}}} - 20*{{{d/4}}} = 20*.45
Cancel the denominators and you have
8d - 5d = 9
3d = 9
d = 9/3
d = 3 km is the distance</PRE>