Joelle started jogging from the boutique to the garden at a speed of 100 m/min at 8 a.m. Her sister started jogging from the boutique later. They were beside each other at 8.44 a.m. and her sister reached the garden at 9 a.m. while Joelle was still 1600 m away. If both of them travelled at a constant speed throughout the journey, what time did her sister leave the boutique?
1 h = 60 min

From 8 a.m. to 9 a.m. = 1 h
From 8.44 a.m. to 9 a.m. = 16 min

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

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

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

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

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

Time that Joelle's sister left the boutique:
38 min before 9 a.m. = 8.22 a.m.

Answer(s): 8.22 a.m.