At 7 a.m., Sarah and Jen raced off together from the starting point of a track. Sarah ran at an average speed of 3 m/s. Jen ran at an average speed of 4 m/s. Upon reaching the end of the track, Jen rested for 5 minutes. She then immediately ran back along the same route at 4 m/s. At 7.40 a.m., Sarah met Jen.

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 7 a.m. to 7.40 a.m. = 40 min

Duration that Sarah ran = 40 min
Duration that Jen ran = 40 -  5 = 35 min

1 min = 60 s

35 min = 35 x 60 = 2100 s
40 min = 40 x 60 = 2400 s

Distance that Sarah ran
= 3 x 2400
= 7200 m

Distance that Jen ran
= 4 x 2100
= 8400 m

Distance that Sarah and Jen ran
= 7200 + 8400
= 15600 m

1000 m = 1 km

15600 m = 15600 ÷ 1000 = 15.6 km

(b)
Length of the trail
= 15.6 ÷ 2
= 7.8 km

Answer(s): (a) 15.6 km; (b) 7.8 km