Winnie started jogging from the mosque to the reservoir at a speed of 96 m/min at 5 a.m. Her sister started jogging from the mosque later. They were beside each other at 5.35 a.m. and her sister reached the reservoir at 6 a.m. while Winnie was still 1800 m away. If both of them travelled at a constant speed throughout the journey, what time did her sister leave the mosque?
1 h = 60 min

From 5 a.m. to 6 a.m. = 1 h
From 5.35 a.m. to 6 a.m. = 25 min

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

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

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

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

Duration that Winnie's sister took to jog to the reservoir
= 7560 ÷ 168
= 45 min

Time that Winnie's sister left the mosque:
45 min before 6 a.m. = 5.15 a.m.

Answer(s): 5.15 a.m.