PSLE
Della and Erny started jogging from the same point of the 8 km track round a lake. They started at the same time but in opposite directions. Della jogged past Erny after 5 km. Both of them did not change their speeds throughout. Della took 20 min to complete one round. What was Erny's jogging speed in m/min?
Distance that Erny jogged when they passed each other
= 8 - 5
= 3 km

Time that Della took to jog 8 km = 20 min

Time that Della took to jog 1 km
= 20 ÷ 8
= 2.5 min

Time that Della took to jog 5 km
= 5 x 2.5
= 12.5 min

When Della took 12.5 min to jog 5 km, Erny took the same time to jog 3 km.

1 km = 1000 m
3 km = 3000 m

Erny's jogging speed
= 3000 ÷ 12.5
= 240 m/min

Answer(s): 240 m/min