At 11 a.m., Risa and Xylia raced off together from the starting point of a course. Risa ran at an average speed of 3 m/s. Xylia ran at an average speed of 4 m/s. Upon reaching the end of the course, Xylia rested for 4 minutes. She then immediately ran back along the same route at 4 m/s. At 11.40 a.m., Risa met Xylia.

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 11.40 a.m. = 40 min

Duration that Risa ran = 40 min
Duration that Xylia ran = 40 -  4 = 36 min

1 min = 60 s

36 min = 36 x 60 = 2160 s
40 min = 40 x 60 = 2400 s

Distance that Risa ran
= 3 x 2400
= 7200 m

Distance that Xylia ran
= 4 x 2160
= 8640 m

Distance that Risa and Xylia ran
= 7200 + 8640
= 15840 m

1000 m = 1 km

15840 m = 15840 ÷ 1000 = 15.84 km

(b)
Length of the trail
= 15.84 ÷ 2
= 7.92 km

Answer(s): (a) 15.84 km; (b) 7.92 km