Hazel started jogging from the salon to the reservoir at a speed of 105 m/min at 5 a.m. Her sister started jogging from the salon later. They were beside each other at 5.45 a.m. and her sister reached the reservoir at 6 a.m. while Hazel was still 1800 m away. If both of them travelled at a constant speed throughout the journey, what time did her sister leave the salon?
1 h = 60 min

From 5 a.m. to 6 a.m. = 1 h
From 5.45 a.m. to 6 a.m. = 15 min

Distance between the salon and the reservoir
= 60 x 105 + 1800
= 6300 + 1800
= 8100 m

Distance that Hazel's sister had to cover to catch up with Hazel
= 45 x 105
= 4725 m

Distance that Hazel's sister travelled to the reservoir after catching up with Hazel
= 8100 - 4725
= 3375 m

Since Hazel's sister jogged 3375 m in 45 min,
Hazel's sister average speed
= 3375 ÷ 15
= 225 m/min

Duration that Hazel's sister took to jog to the reservoir
= 8100 ÷ 225
= 36 min

Time that Hazel's sister left the salon:
36 min before 6 a.m. = 5.24 a.m.

Answer(s): 5.24 a.m.