Perry, Eric and Paul started walking at the same time from the same starting point round a circular track. Paul walked in the clockwise direction. Perry and Eric walked in an anti-clockwise direction. Paul took 12 min to complete each round. He met Perry after every 2 minutes. He met Eric after every 4 minutes. The three friends kept to their respective speeds throughout their walk.

1. How many rounds did Paul complete in 1 h?
2. When Paul and Perry met again at the starting point after 1 h, Eric had completed 2.4 km. Find the circumference of the circular track in metres.

(a)
1 h = 60 min

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

(b)
Paul took 12 min to complete 1 round
1 min = ¹₁₂ of circular track = 1 u
12 min = ¹²₁₂ of circular track = 12 u

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

Paul's distance : Perry's distance
2 : 12 - 2
2 : 10

Paul's distance : Eric's distance
4 : 12 - 4
4 : 8

Paul	Perry	Eric
2x2	10x2
4x1		8x1
4	20	8

The distance of Paul is the repeated identity. 
LCM of 2 and 4 = 4

In 1 h
Paul's rounds : Perry's rounds : Eric's rounds
4 : 20 : 8

Distance that Eric completed in 1 h = 2.4 km

8 rounds = 2.4 km = 2400 m

1 round = 2400 ÷ 8 = 300 m

Circumference of the circular track = 300 m

Answer(s): (a) 5; (b) 300 m