Min started jogging from the mosque to the reservoir at a speed of 105 m/min at 6 a.m. Her cousin started jogging from the mosque later. They were beside each other at 6.40 a.m. and her cousin reached the reservoir at 7 a.m. while Min was still 1900 m away. If both of them travelled at a constant speed throughout the journey, what time did her cousin leave the mosque?
1 h = 60 min

From 6 a.m. to 7 a.m. = 1 h
From 6.40 a.m. to 7 a.m. = 20 min

Distance between the mosque and the reservoir
= 60 x 105 + 1900
= 6300 + 1900
= 8200 m

Distance that Min's cousin had to cover to catch up with Min
= 40 x 105
= 4200 m

Distance that Min's cousin travelled to the reservoir after catching up with Min
= 8200 - 4200
= 4000 m

Since Min's cousin jogged 4000 m in 40 min,
Min's cousin average speed
= 4000 ÷ 20
= 200 m/min

Duration that Min's cousin took to jog to the reservoir
= 8200 ÷ 200
= 41 min

Time that Min's cousin left the mosque:
41 min before 7 a.m. = 6.19 a.m.

Answer(s): 6.19 a.m.