At 9 a.m., Risa and Nora raced off together from the starting point of a route. Risa ran at an average speed of 1 m/s. Nora ran at an average speed of 3 m/s. Upon reaching the end of the route, Nora rested for 4 minutes. She then immediately ran back along the same route at 3 m/s. At 9.45 a.m., Risa met Nora.

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 9.45 a.m. = 45 min

Duration that Risa ran = 45 min
Duration that Nora ran = 45 -  4 = 41 min

1 min = 60 s

41 min = 41 x 60 = 2460 s
45 min = 45 x 60 = 2700 s

Distance that Risa ran
= 1 x 2700
= 2700 m

Distance that Nora ran
= 3 x 2460
= 7380 m

Distance that Risa and Nora ran
= 2700 + 7380
= 10080 m

1000 m = 1 km

10080 m = 10080 ÷ 1000 = 10.08 km

(b)
Length of the trail
= 10.08 ÷ 2
= 5.04 km

Answer(s): (a) 10.08 km; (b) 5.04 km