Risa and Shiyun started off at the same spot and ran at average speeds round a 4-km circular path. Risa took 24 minutes to complete each round. Shiyun completed each round in 30 minutes.
- How far ahead of Shiyun would Risa be after 3 minute? Express your answer in metres.
- How long would it take Risa to meet Shiyun for the first time?
- How many rounds would Risa have completed by then?
(a)
Risa's speed =
424 =
16 km/min
Shiyun's speed =
215 km/min
Difference in speeds
=
16 -
215=
530 -
430=
130 km/min
Distance between Risa and Shiyun after 3 min
= 3 x
130=
330 km
1 km = 1000 m
330 km =
330 x 1000 = 100
(b)
LCM of 24 and 30 = 120
60 min = 1 h
120 min = 120 ÷ 60 = 2
Risa and Shiyun will meet for the first time after 2 h.
(c)
Rounds Risa completed
= 120 ÷ 24
= 5
Answer(s): (a) 100 m; (b) 2 h; (c) 5