Nora started jogging from the clinic to the nature reserve at a speed of 105 m/min at 8 a.m. Her brother started jogging from the clinic later. They were beside each other at 8.41 a.m. and her brother reached the nature reserve at 9 a.m. while Nora was still 1900 m away. If both of them travelled at a constant speed throughout the journey, what time did her brother leave the clinic?
1 h = 60 min

From 8 a.m. to 9 a.m. = 1 h
From 8.41 a.m. to 9 a.m. = 19 min

Distance between the clinic and the nature reserve
= 60 x 105 + 1900
= 6300 + 1900
= 8200 m

Distance that Nora's brother had to cover to catch up with Nora
= 41 x 105
= 4305 m

Distance that Nora's brother travelled to the nature reserve after catching up with Nora
= 8200 - 4305
= 3895 m

Since Nora's brother jogged 3895 m in 41 min,
Nora's brother average speed
= 3895 ÷ 19
= 205 m/min

Duration that Nora's brother took to jog to the nature reserve
= 8200 ÷ 205
= 40 min

Time that Nora's brother left the clinic:
40 min before 9 a.m. = 8.20 a.m.

Answer(s): 8.20 a.m.