Cindy started jogging from the cinema to the garden at a speed of 100 m/min at 7 a.m. Her sister started jogging from the cinema later. They were beside each other at 7.44 a.m. and her sister reached the garden at 8 a.m. while Cindy was still 1600 m away. If both of them travelled at a constant speed throughout the journey, what time did her sister leave the cinema?
1 h = 60 min

From 7 a.m. to 8 a.m. = 1 h
From 7.44 a.m. to 8 a.m. = 16 min

Distance between the cinema and the garden
= 60 x 100 + 1600
= 6000 + 1600
= 7600 m

Distance that Cindy's sister had to cover to catch up with Cindy
= 44 x 100
= 4400 m

Distance that Cindy's sister travelled to the garden after catching up with Cindy
= 7600 - 4400
= 3200 m

Since Cindy's sister jogged 3200 m in 44 min,
Cindy's sister average speed
= 3200 ÷ 16
= 200 m/min

Duration that Cindy's sister took to jog to the garden
= 7600 ÷ 200
= 38 min

Time that Cindy's sister left the cinema:
38 min before 8 a.m. = 7.22 a.m.

Answer(s): 7.22 a.m.