Roshel started jogging from the clinic to the park at a speed of 100 m/min at 8 a.m. Her cousin started jogging from the clinic later. They were beside each other at 8.40 a.m. and her cousin reached the park at 9 a.m. while Roshel was still 1200 m away. If both of them travelled at a constant speed throughout the journey, what time did her cousin leave the clinic?
1 h = 60 min

From 8 a.m. to 9 a.m. = 1 h
From 8.40 a.m. to 9 a.m. = 20 min

Distance between the clinic and the park
= 60 x 100 + 1200
= 6000 + 1200
= 7200 m

Distance that Roshel's cousin had to cover to catch up with Roshel
= 40 x 100
= 4000 m

Distance that Roshel's cousin travelled to the park after catching up with Roshel
= 7200 - 4000
= 3200 m

Since Roshel's cousin jogged 3200 m in 40 min,
Roshel's cousin average speed
= 3200 ÷ 20
= 160 m/min

Duration that Roshel's cousin took to jog to the park
= 7200 ÷ 160
= 45 min

Time that Roshel's cousin left the clinic:
45 min before 9 a.m. = 8.15 a.m.

Answer(s): 8.15 a.m.