PSLE
Sonia and Mary 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. Sonia jogged past Mary after 10 km. Both of them did not change their speeds throughout. Sonia took 30 min to complete one round. What was Mary's jogging speed in m/min?
Distance that Mary jogged when they passed each other
= 15 - 10
= 5 km

Time that Sonia took to jog 15 km = 30 min

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

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

When Sonia took 20 min to jog 10 km, Mary took the same time to jog 5 km.

1 km = 1000 m
5 km = 5000 m

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

Answer(s): 250 m/min