Jade started jogging from the bank to the garden at a speed of 96 m/min at 6 a.m. Her sister started jogging from the bank later. They were beside each other at 6.45 a.m. and her sister reached the garden at 7 a.m. while Jade was still 1800 m away. If both of them travelled at a constant speed throughout the journey, what time did her sister leave the bank?
1 h = 60 min

From 6 a.m. to 7 a.m. = 1 h
From 6.45 a.m. to 7 a.m. = 15 min

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

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

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

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

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

Time that Jade's sister left the bank:
35 min before 7 a.m. = 6.25 a.m.

Answer(s): 6.25 a.m.