PSLE
Ella and Mary started jogging from the same point of the 15 km track round a lake. They started at the same time but in opposite directions. Ella jogged past Mary after 12 km. Both of them did not change their speeds throughout. Ella took 15 min to complete one round. What was Mary's jogging speed in m/min?
Distance that Mary jogged when they passed each other
= 15 - 12
= 3 km

Time that Ella took to jog 15 km = 15 min

Time that Ella took to jog 1 km
= 15 ÷ 15
= 1 min

Time that Ella took to jog 12 km
= 12 x 1
= 12 min

When Ella took 12 min to jog 12 km, Mary took the same time to jog 3 km.

1 km = 1000 m
3 km = 3000 m

Mary's jogging speed
= 3000 ÷ 12
= 250 m/min

Answer(s): 250 m/min