Justin, Owen and Henry started walking at the same time from the same starting point round a circular track. Henry walked in the clockwise direction. Justin and Owen walked in an anti-clockwise direction. Henry took 6 min to complete each round. He met Justin after every 3 minutes. He met Owen after every 5 minutes. The three friends kept to their respective speeds throughout their walk.

1. How many rounds did Henry complete in 1 h?
2. When Henry and Justin met again at the starting point after 1 h, Owen had completed 1.8 km. Find the circumference of the circular track in metres.

(a)
1 h = 60 min

Number of rounds that Henry completed in 1 h
= 60 ÷ 6
= 10

(b)
Henry took 6 min to complete 1 round
1 min = ¹₆ of circular track = 1 u
6 min = ⁶₆ of circular track = 6 u

Henry's distance is the repeated identity.
Make Henry's distance the same.

Henry's distance : Justin's distance
3 : 6 - 3
3 : 3

Henry's distance : Owen's distance
5 : 6 - 5
5 : 1

Henry	Justin	Owen
3x5	3x5
5x3		1x3
15	15	3

The distance of Henry is the repeated identity. 
LCM of 3 and 5 = 15

In 1 h
Henry's rounds : Justin's rounds : Owen's rounds
15 : 15 : 3

Distance that Owen completed in 1 h = 1.8 km

3 rounds = 1.8 km = 1800 m

1 round = 1800 ÷ 3 = 600 m

Circumference of the circular track = 600 m

Answer(s): (a) 10; (b) 600 m