Cody, Albert and Rael started walking at the same time from the same starting point round a circular track. Rael walked in the clockwise direction. Cody and Albert walked in an anti-clockwise direction. Rael took 12 min to complete each round. He met Cody after every 2 minutes. He met Albert after every 7 minutes. The three friends kept to their respective speeds throughout their walk.
- How many rounds did Rael complete in 1 h?
- When Rael and Cody met again at the starting point after 1 h, Albert had completed 2.9 km. Find the circumference of the circular track in metres.
(a)
1 h = 60 min
Number of rounds that Rael completed in 1 h
= 60 ÷ 12
= 5
(b)
Rael took 12 min to complete 1 round
1 min =
112 of circular track = 1 u
12 min =
1212 of circular track = 12 u
Rael's distance is the repeated identity.
Make Rael's distance the same.
Rael's distance : Cody's distance
2 : 12 - 2
2 : 10
Rael's distance : Albert's distance
7 : 12 - 7
7 : 5
Rael |
Cody |
Albert |
2x7 |
10x7 |
|
7x2 |
|
5x2 |
14 |
70 |
10 |
The distance of Rael is the repeated identity.
LCM of 2 and 7 = 14
In 1 h
Rael's rounds : Cody's rounds : Albert's rounds
14 : 70 : 10
Distance that Albert completed in 1 h = 2.9 km
10 rounds = 2.9 km = 2900 m
1 round = 2900 ÷ 10 = 290 m
Circumference of the circular track = 290 m
Answer(s): (a) 5; (b) 290 m