Abi started jogging from the cinema to the nature reserve at a speed of 105 m/min at 6 a.m. Her brother started jogging from the cinema later. They were beside each other at 6.45 a.m. and her brother reached the nature reserve at 7 a.m. while Abi was still 1800 m away. If both of them travelled at a constant speed throughout the journey, what time did her brother leave the cinema?
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 cinema and the nature reserve
= 60 x 105 + 1800
= 6300 + 1800
= 8100 m

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

Distance that Abi's brother travelled to the nature reserve after catching up with Abi
= 8100 - 4725
= 3375 m

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

Duration that Abi's brother took to jog to the nature reserve
= 8100 ÷ 225
= 36 min

Time that Abi's brother left the cinema:
36 min before 7 a.m. = 6.24 a.m.

Answer(s): 6.24 a.m.