Cindy started jogging from the museum to the nature reserve at a speed of 108 m/min at 9 a.m. Her sister started jogging from the museum later. They were beside each other at 9.35 a.m. and her sister reached the nature reserve at 10 a.m. while Cindy was still 1800 m away. If both of them travelled at a constant speed throughout the journey, what time did her sister leave the museum?
1 h = 60 min

From 9 a.m. to 10 a.m. = 1 h
From 9.35 a.m. to 10 a.m. = 25 min

Distance between the museum and the nature reserve
= 60 x 108 + 1800
= 6480 + 1800
= 8280 m

Distance that Cindy's sister had to cover to catch up with Cindy
= 35 x 108
= 3780 m

Distance that Cindy's sister travelled to the nature reserve after catching up with Cindy
= 8280 - 3780
= 4500 m

Since Cindy's sister jogged 4500 m in 35 min,
Cindy's sister average speed
= 4500 ÷ 25
= 180 m/min

Duration that Cindy's sister took to jog to the nature reserve
= 8280 ÷ 180
= 46 min

Time that Cindy's sister left the museum:
46 min before 10 a.m. = 9.14 a.m.

Answer(s): 9.14 a.m.