Simon, Bobby and Jack started walking at the same time from the same starting point round a circular track. Jack walked in the clockwise direction. Simon and Bobby walked in an anti-clockwise direction. Jack took 6 min to complete each round. He met Simon after every 2 minutes. He met Bobby after every 5 minutes. The three friends kept to their respective speeds throughout their walk.

1. How many rounds did Jack complete in 1 h?
2. When Jack and Simon met again at the starting point after 1 h, Bobby had completed 1.6 km. Find the circumference of the circular track in metres.

(a)
1 h = 60 min

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

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

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

Jack's distance : Simon's distance
2 : 6 - 2
2 : 4

Jack's distance : Bobby's distance
5 : 6 - 5
5 : 1

Jack	Simon	Bobby
2x5	4x5
5x2		1x2
10	20	2

The distance of Jack is the repeated identity. 
LCM of 2 and 5 = 10

In 1 h
Jack's rounds : Simon's rounds : Bobby's rounds
10 : 20 : 2

Distance that Bobby completed in 1 h = 1.6 km

2 rounds = 1.6 km = 1600 m

1 round = 1600 ÷ 2 = 800 m

Circumference of the circular track = 800 m

Answer(s): (a) 10; (b) 800 m