Yoko started jogging from the cafe to the reservoir at a speed of 96 m/min at 7 a.m. Her cousin started jogging from the cafe later. They were beside each other at 7.35 a.m. and her cousin reached the reservoir at 8 a.m. while Yoko was still 1800 m away. If both of them travelled at a constant speed throughout the journey, what time did her cousin leave the cafe?
1 h = 60 min

From 7 a.m. to 8 a.m. = 1 h
From 7.35 a.m. to 8 a.m. = 25 min

Distance between the cafe and the reservoir
= 60 x 96 + 1800
= 5760 + 1800
= 7560 m

Distance that Yoko's cousin had to cover to catch up with Yoko
= 35 x 96
= 3360 m

Distance that Yoko's cousin travelled to the reservoir after catching up with Yoko
= 7560 - 3360
= 4200 m

Since Yoko's cousin jogged 4200 m in 35 min,
Yoko's cousin average speed
= 4200 ÷ 25
= 168 m/min

Duration that Yoko's cousin took to jog to the reservoir
= 7560 ÷ 168
= 45 min

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

Answer(s): 7.15 a.m.