PSLE
Elsa and Della started jogging from the same point of the 15 km track round a housing estate. They started at the same time but in opposite directions. Elsa jogged past Della after 10 km. Both of them did not change their speeds throughout. Elsa took 30 min to complete one round. What was Della's jogging speed in m/min?
Distance that Della jogged when they passed each other
= 15 - 10
= 5 km

Time that Elsa took to jog 15 km = 30 min

Time that Elsa took to jog 1 km
= 30 ÷ 15
= 2 min

Time that Elsa took to jog 10 km
= 10 x 2
= 20 min

When Elsa took 20 min to jog 10 km, Della took the same time to jog 5 km.

1 km = 1000 m
5 km = 5000 m

Della's jogging speed
= 5000 ÷ 20
= 250 m/min

Answer(s): 250 m/min