PSLE
Della and Leah started jogging from the same point of the 12 km track round a lake. They started at the same time but in opposite directions. Della jogged past Leah after 8 km. Both of them did not change their speeds throughout. Della took 30 min to complete one round. What was Leah's jogging speed in m/min?
Distance that Leah jogged when they passed each other
= 12 - 8
= 4 km

Time that Della took to jog 12 km = 30 min

Time that Della took to jog 1 km
= 30 ÷ 12
= 2.5 min

Time that Della took to jog 8 km
= 8 x 2.5
= 20 min

When Della took 20 min to jog 8 km, Leah took the same time to jog 4 km.

1 km = 1000 m
4 km = 4000 m

Leah's jogging speed
= 4000 ÷ 20
= 200 m/min

Answer(s): 200 m/min