Jen started jogging from the library to the reservoir at a speed of 110 m/min at 6 a.m. Her brother started jogging from the library later. They were beside each other at 6.32 a.m. and her brother reached the reservoir at 7 a.m. while Jen was still 1400 m away. If both of them travelled at a constant speed throughout the journey, what time did her brother leave the library?
1 h = 60 min

From 6 a.m. to 7 a.m. = 1 h
From 6.32 a.m. to 7 a.m. = 28 min

Distance between the library and the reservoir
= 60 x 110 + 1400
= 6600 + 1400
= 8000 m

Distance that Jen's brother had to cover to catch up with Jen
= 32 x 110
= 3520 m

Distance that Jen's brother travelled to the reservoir after catching up with Jen
= 8000 - 3520
= 4480 m

Since Jen's brother jogged 4480 m in 32 min,
Jen's brother average speed
= 4480 ÷ 28
= 160 m/min

Duration that Jen's brother took to jog to the reservoir
= 8000 ÷ 160
= 50 min

Time that Jen's brother left the library:
50 min before 7 a.m. = 6.10 a.m.

Answer(s): 6.10 a.m.