Ivory started jogging from the salon to the reservoir at a speed of 105 m/min at 7 a.m. Her cousin started jogging from the salon later. They were beside each other at 7.36 a.m. and her cousin reached the reservoir at 8 a.m. while Ivory was still 1800 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 7 a.m. to 8 a.m. = 1 h
From 7.36 a.m. to 8 a.m. = 24 min

Distance between the salon and the reservoir
= 60 x 105 + 1800
= 6300 + 1800
= 8100 m

Distance that Ivory's cousin had to cover to catch up with Ivory
= 36 x 105
= 3780 m

Distance that Ivory's cousin travelled to the reservoir after catching up with Ivory
= 8100 - 3780
= 4320 m

Since Ivory's cousin jogged 4320 m in 36 min,
Ivory's cousin average speed
= 4320 ÷ 24
= 180 m/min

Duration that Ivory's cousin took to jog to the reservoir
= 8100 ÷ 180
= 45 min

Time that Ivory's cousin left the salon:
45 min before 8 a.m. = 7.15 a.m.

Answer(s): 7.15 a.m.