Question 1107629

Let the distance covered by the cyclist in 

kilometres be 'd' and time 't'.


Distance = Speed × Time


Distance travelled at a constant speed of 12km/h from A to B is;


d = 12t


Distance travelled on cyclist's return journey is;


d = 18(t-0.25)


* Note that the cyclist increased his speed to 18km/h and therefore covered the same distance 15 minutes less.


15 minutes in hours is 15/60 = 1/4 or 0.25


12t = 18(t-0.25)


12t= 18t-4.5


6t = 4.5


t = 0.75 or 3/4 hours


Distance between points A and B therefore is;


12×0.75 = 9 km or 18×(0.75-0.25) = 18×0.5 = 9km