Ethan, Eric and Will started walking at the same time from the same starting point round a circular track. Will walked in the clockwise direction. Ethan and Eric walked in an anti-clockwise direction. Will took 5 min to complete each round. He met Ethan after every 3 minutes. He met Eric after every 4 minutes. The three friends kept to their respective speeds throughout their walk.

1. How many rounds did Will complete in 1 h?
2. When Will and Ethan met again at the starting point after 1 h, Eric had completed 1.5 km. Find the circumference of the circular track in metres.

(a)
1 h = 60 min

Number of rounds that Will completed in 1 h
= 60 ÷ 5
= 12

(b)
Will took 5 min to complete 1 round
1 min = ¹₅ of circular track = 1 u
5 min = ⁵₅ of circular track = 5 u

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

Will's distance : Ethan's distance
3 : 5 - 3
3 : 2

Will's distance : Eric's distance
4 : 5 - 4
4 : 1

Will	Ethan	Eric
3x4	2x4
4x3		1x3
12	8	3

The distance of Will is the repeated identity. 
LCM of 3 and 4 = 12

In 1 h
Will's rounds : Ethan's rounds : Eric's rounds
12 : 8 : 3

Distance that Eric completed in 1 h = 1.5 km

3 rounds = 1.5 km = 1500 m

1 round = 1500 ÷ 3 = 500 m

Circumference of the circular track = 500 m

Answer(s): (a) 12; (b) 500 m