PSLE
Riley and Elsa started jogging from the same point of the 12 km track round a park. They started at the same time but in opposite directions. Riley jogged past Elsa after 10 km. Both of them did not change their speeds throughout. Riley took 15 min to complete one round. What was Elsa's jogging speed in m/min?
Distance that Elsa jogged when they passed each other
= 12 - 10
= 2 km

Time that Riley took to jog 12 km = 15 min

Time that Riley took to jog 1 km
= 15 ÷ 12
= 1.25 min

Time that Riley took to jog 10 km
= 10 x 1.25
= 12.5 min

When Riley took 12.5 min to jog 10 km, Elsa took the same time to jog 2 km.

1 km = 1000 m
2 km = 2000 m

Elsa's jogging speed
= 2000 ÷ 12.5
= 160 m/min

Answer(s): 160 m/min