Tina started jogging from the park to the reservoir at a speed of 105 m/min at 7 a.m. Her cousin started jogging from the park later. They were beside each other at 7.45 a.m. and her cousin reached the reservoir at 8 a.m. while Tina was still 1800 m away. If both of them travelled at a constant speed throughout the journey, what time did her cousin leave the park?
1 h = 60 min

From 7 a.m. to 8 a.m. = 1 h
From 7.45 a.m. to 8 a.m. = 15 min

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

Distance that Tina's cousin had to cover to catch up with Tina
= 45 x 105
= 4725 m

Distance that Tina's cousin travelled to the reservoir after catching up with Tina
= 8100 - 4725
= 3375 m

Since Tina's cousin jogged 3375 m in 45 min,
Tina's cousin average speed
= 3375 ÷ 15
= 225 m/min

Duration that Tina's cousin took to jog to the reservoir
= 8100 ÷ 225
= 36 min

Time that Tina's cousin left the park:
36 min before 8 a.m. = 7.24 a.m.

Answer(s): 7.24 a.m.