Risa started jogging from the florist to the park at a speed of 115 m/min at 6 a.m. Her cousin started jogging from the florist later. They were beside each other at 6.35 a.m. and her cousin reached the park at 7 a.m. while Risa was still 1500 m away. If both of them travelled at a constant speed throughout the journey, what time did her cousin leave the florist?
1 h = 60 min

From 6 a.m. to 7 a.m. = 1 h
From 6.35 a.m. to 7 a.m. = 25 min

Distance between the florist and the park
= 60 x 115 + 1500
= 6900 + 1500
= 8400 m

Distance that Risa's cousin had to cover to catch up with Risa
= 35 x 115
= 4025 m

Distance that Risa's cousin travelled to the park after catching up with Risa
= 8400 - 4025
= 4375 m

Since Risa's cousin jogged 4375 m in 35 min,
Risa's cousin average speed
= 4375 ÷ 25
= 175 m/min

Duration that Risa's cousin took to jog to the park
= 8400 ÷ 175
= 48 min

Time that Risa's cousin left the florist:
48 min before 7 a.m. = 6.12 a.m.

Answer(s): 6.12 a.m.