Jeremy, Vincent and Tommy started walking at the same time from the same starting point round a circular track. Tommy walked in the clockwise direction. Jeremy and Vincent walked in an anti-clockwise direction. Tommy took 12 min to complete each round. He met Jeremy after every 2 minutes. He met Vincent after every 7 minutes. The three friends kept to their respective speeds throughout their walk.
- How many rounds did Tommy complete in 1 h?
- When Tommy and Jeremy met again at the starting point after 1 h, Vincent had completed 2.1 km. Find the circumference of the circular track in metres.
(a)
1 h = 60 min
Number of rounds that Tommy completed in 1 h
= 60 ÷ 12
= 5
(b)
Tommy took 12 min to complete 1 round
1 min =
112 of circular track = 1 u
12 min =
1212 of circular track = 12 u
Tommy's distance is the repeated identity.
Make Tommy's distance the same.
Tommy's distance : Jeremy's distance
2 : 12 - 2
2 : 10
Tommy's distance : Vincent's distance
7 : 12 - 7
7 : 5
Tommy |
Jeremy |
Vincent |
2x7 |
10x7 |
|
7x2 |
|
5x2 |
14 |
70 |
10 |
The distance of Tommy is the repeated identity.
LCM of 2 and 7 = 14
In 1 h
Tommy's rounds : Jeremy's rounds : Vincent's rounds
14 : 70 : 10
Distance that Vincent completed in 1 h = 2.1 km
10 rounds = 2.1 km = 2100 m
1 round = 2100 ÷ 10 = 210 m
Circumference of the circular track = 210 m
Answer(s): (a) 5; (b) 210 m