At 9 a.m., Usha and Ivory raced off together from the starting point of a path. Usha ran at an average speed of 1 m/s. Ivory ran at an average speed of 4 m/s. Upon reaching the end of the path, Ivory rested for 5 minutes. She then immediately ran back along the same route at 4 m/s. At 9.30 a.m., Usha met Ivory.

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 9.30 a.m. = 30 min

Duration that Usha ran = 30 min
Duration that Ivory ran = 30 -  5 = 25 min

1 min = 60 s

25 min = 25 x 60 = 1500 s
30 min = 30 x 60 = 1800 s

Distance that Usha ran
= 1 x 1800
= 1800 m

Distance that Ivory ran
= 4 x 1500
= 6000 m

Distance that Usha and Ivory ran
= 1800 + 6000
= 7800 m

1000 m = 1 km

7800 m = 7800 ÷ 1000 = 7.8 km

(b)
Length of the trail
= 7.8 ÷ 2
= 3.9 km

Answer(s): (a) 7.8 km; (b) 3.9 km