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

1. How many rounds did Vaidev complete in 1 h?
2. When Vaidev and Cody met again at the starting point after 1 h, Ken had completed 1.7 km. Find the circumference of the circular track in metres.

(a)
1 h = 60 min

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

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

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

Vaidev's distance : Cody's distance
4 : 6 - 4
4 : 2

Vaidev's distance : Ken's distance
5 : 6 - 5
5 : 1

Vaidev	Cody	Ken
4x5	2x5
5x4		1x4
20	10	4

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

In 1 h
Vaidev's rounds : Cody's rounds : Ken's rounds
20 : 10 : 4

Distance that Ken completed in 1 h = 1.7 km

4 rounds = 1.7 km = 1700 m

1 round = 1700 ÷ 4 = 425 m

Circumference of the circular track = 425 m

Answer(s): (a) 10; (b) 425 m