Opal started jogging from the hypermart to the nature reserve at a speed of 110 m/min at 8 a.m. Her cousin started jogging from the hypermart later. They were beside each other at 8.42 a.m. and her cousin reached the nature reserve at 9 a.m. while Opal was still 1800 m away. If both of them travelled at a constant speed throughout the journey, what time did her cousin leave the hypermart?
1 h = 60 min

From 8 a.m. to 9 a.m. = 1 h
From 8.42 a.m. to 9 a.m. = 18 min

Distance between the hypermart and the nature reserve
= 60 x 110 + 1800
= 6600 + 1800
= 8400 m

Distance that Opal's cousin had to cover to catch up with Opal
= 42 x 110
= 4620 m

Distance that Opal's cousin travelled to the nature reserve after catching up with Opal
= 8400 - 4620
= 3780 m

Since Opal's cousin jogged 3780 m in 42 min,
Opal's cousin average speed
= 3780 ÷ 18
= 210 m/min

Duration that Opal's cousin took to jog to the nature reserve
= 8400 ÷ 210
= 40 min

Time that Opal's cousin left the hypermart:
40 min before 9 a.m. = 8.20 a.m.

Answer(s): 8.20 a.m.