At 9 a.m., Mary and Dana raced off together from the starting point of a track. Mary ran at an average speed of 3 m/s. Dana ran at an average speed of 4 m/s. Upon reaching the end of the track, Dana rested for 4 minutes. She then immediately ran back along the same route at 4 m/s. At 9.40 a.m., Mary met Dana.

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 9.40 a.m. = 40 min

Duration that Mary ran = 40 min
Duration that Dana 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 Mary ran
= 3 x 2400
= 7200 m

Distance that Dana ran
= 4 x 2160
= 8640 m

Distance that Mary and Dana 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