At 9 a.m., Marion and Risa raced off together from the starting point of a track. Marion ran at an average speed of 1 m/s. Risa ran at an average speed of 3 m/s. Upon reaching the end of the track, Risa rested for 5 minutes. She then immediately ran back along the same route at 3 m/s. At 9.25 a.m., Marion met Risa.

1. Find the total distance covered by the two runners when they met each other. Express your answer in km.
2. Find the length of the trail in km.

(a)
From 9 a.m. to 9.25 a.m. = 25 min

Duration that Marion ran = 25 min
Duration that Risa ran = 25 -  5 = 20 min

1 min = 60 s

20 min = 20 x 60 = 1200 s
25 min = 25 x 60 = 1500 s

Distance that Marion ran
= 1 x 1500
= 1500 m

Distance that Risa ran
= 3 x 1200
= 3600 m

Distance that Marion and Risa ran
= 1500 + 3600
= 5100 m

1000 m = 1 km

5100 m = 5100 ÷ 1000 = 5.1 km

(b)
Length of the trail
= 5.1 ÷ 2
= 2.55 km

Answer(s): (a) 5.1 km; (b) 2.55 km