Zane, Bobby and John started walking at the same time from the same starting point round a circular track. John walked in the clockwise direction. Zane and Bobby walked in an anti-clockwise direction. John took 6 min to complete each round. He met Zane after every 4 minutes. He met Bobby after every 5 minutes. The three friends kept to their respective speeds throughout their walk.

1. How many rounds did John complete in 1 h?
2. When John and Zane met again at the starting point after 1 h, Bobby had completed 1.4 km. Find the circumference of the circular track in metres.

(a)
1 h = 60 min

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

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

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

John's distance : Zane's distance
4 : 6 - 4
4 : 2

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

John	Zane	Bobby
4x5	2x5
5x4		1x4
20	10	4

The distance of John is the repeated identity. 
LCM of 4 and 5 = 20

In 1 h
John's rounds : Zane's rounds : Bobby's rounds
20 : 10 : 4

Distance that Bobby completed in 1 h = 1.4 km

4 rounds = 1.4 km = 1400 m

1 round = 1400 ÷ 4 = 350 m

Circumference of the circular track = 350 m

Answer(s): (a) 10; (b) 350 m