average speed

Question

Car A left Melbourne for Adelaide at 11:00 am and travelled at an average aped of 70 km per hour. Car B left melbourne for Adelaide at 1:00 on the same day and travelled at an average speed of 90kmph at what time does car B catch car A

Answer 1

d = rt

 

Car A:  d = 70t

Car B:  d = 90(t-2)    since left 2 hours later

 

We want to know when the distances are equal

 

90(t-2) = 70t

90t - 180 = 70t

20t = 180

t = 9 hours

 

9 hours from the time car A left which was 11:00 a.m.

They meet at 8:00 p.m.