At 7 a.m., Risa and Yoko raced off together from the starting point of a pathway. Risa ran at an average speed of 1 m/s. Yoko ran at an average speed of 2 m/s. Upon reaching the end of the pathway, Yoko rested for 5 minutes. She then immediately ran back along the same route at 2 m/s. At 7.50 a.m., Risa met Yoko.

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 7.50 a.m. = 50 min

Duration that Risa ran = 50 min
Duration that Yoko ran = 50 -  5 = 45 min

1 min = 60 s

45 min = 45 x 60 = 2700 s
50 min = 50 x 60 = 3000 s

Distance that Risa ran
= 1 x 3000
= 3000 m

Distance that Yoko ran
= 2 x 2700
= 5400 m

Distance that Risa and Yoko ran
= 3000 + 5400
= 8400 m

1000 m = 1 km

8400 m = 8400 ÷ 1000 = 8.4 km

(b)
Length of the trail
= 8.4 ÷ 2
= 4.2 km

Answer(s): (a) 8.4 km; (b) 4.2 km