Gillian started jogging from the church to the garden at a speed of 96 m/min at 8 a.m. Her sister started jogging from the church later. They were beside each other at 8.45 a.m. and her sister reached the garden at 9 a.m. while Gillian was still 1800 m away. If both of them travelled at a constant speed throughout the journey, what time did her sister leave the church?
1 h = 60 min

From 8 a.m. to 9 a.m. = 1 h
From 8.45 a.m. to 9 a.m. = 15 min

Distance between the church and the garden
= 60 x 96 + 1800
= 5760 + 1800
= 7560 m

Distance that Gillian's sister had to cover to catch up with Gillian
= 45 x 96
= 4320 m

Distance that Gillian's sister travelled to the garden after catching up with Gillian
= 7560 - 4320
= 3240 m

Since Gillian's sister jogged 3240 m in 45 min,
Gillian's sister average speed
= 3240 ÷ 15
= 216 m/min

Duration that Gillian's sister took to jog to the garden
= 7560 ÷ 216
= 35 min

Time that Gillian's sister left the church:
35 min before 9 a.m. = 8.25 a.m.

Answer(s): 8.25 a.m.