Xuan started jogging from the salon to the nature reserve at a speed of 100 m/min at 5 a.m. Her cousin started jogging from the salon later. They were beside each other at 5.44 a.m. and her cousin reached the nature reserve at 6 a.m. while Xuan was still 1600 m away. If both of them travelled at a constant speed throughout the journey, what time did her cousin leave the salon?
1 h = 60 min

From 5 a.m. to 6 a.m. = 1 h
From 5.44 a.m. to 6 a.m. = 16 min

Distance between the salon and the nature reserve
= 60 x 100 + 1600
= 6000 + 1600
= 7600 m

Distance that Xuan's cousin had to cover to catch up with Xuan
= 44 x 100
= 4400 m

Distance that Xuan's cousin travelled to the nature reserve after catching up with Xuan
= 7600 - 4400
= 3200 m

Since Xuan's cousin jogged 3200 m in 44 min,
Xuan's cousin average speed
= 3200 ÷ 16
= 200 m/min

Duration that Xuan's cousin took to jog to the nature reserve
= 7600 ÷ 200
= 38 min

Time that Xuan's cousin left the salon:
38 min before 6 a.m. = 5.22 a.m.

Answer(s): 5.22 a.m.