At 11 a.m., Barbara and Usha raced off together from the starting point of a course. Barbara ran at an average speed of 2 m/s. Usha ran at an average speed of 4 m/s. Upon reaching the end of the course, Usha rested for 5 minutes. She then immediately ran back along the same route at 4 m/s. At 11.25 a.m., Barbara met Usha.

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 11.25 a.m. = 25 min

Duration that Barbara ran = 25 min
Duration that Usha ran = 25 -  5 = 20 min

1 min = 60 s

20 min = 20 x 60 = 1200 s
25 min = 25 x 60 = 1500 s

Distance that Barbara ran
= 2 x 1500
= 3000 m

Distance that Usha ran
= 4 x 1200
= 4800 m

Distance that Barbara and Usha ran
= 3000 + 4800
= 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