At 11 a.m., Anna and Risa raced off together from the starting point of a course. Anna 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 course, Risa rested for 3 minutes. She then immediately ran back along the same route at 3 m/s. At 11.50 a.m., Anna 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 11 a.m. to 11.50 a.m. = 50 min

Duration that Anna ran = 50 min
Duration that Risa ran = 50 -  3 = 47 min

1 min = 60 s

47 min = 47 x 60 = 2820 s
50 min = 50 x 60 = 3000 s

Distance that Anna ran
= 1 x 3000
= 3000 m

Distance that Risa ran
= 3 x 2820
= 8460 m

Distance that Anna and Risa ran
= 3000 + 8460
= 11460 m

1000 m = 1 km

11460 m = 11460 ÷ 1000 = 11.46 km

(b)
Length of the trail
= 11.46 ÷ 2
= 5.73 km

Answer(s): (a) 11.46 km; (b) 5.73 km