PSLE M2009 MATHEMATICS QUESTION

Mei and Lin were in a bicycle race. Mei was travelling at a constant speed of 20km/hr and they both did not change their speed. When Lin completed half the race, Mei was 3.5km ahead. Mei completed the race at 10.45am. What time did Lin complete the race?

Solution:

1st of all, I drew the model, marking out the midpoint.



Then I added in the details, when Lin travelled halfway, Mei was 3.5km ahead of her.



Now, with a distance and a speed, we can now find the time that Mei would have saved, if she was only travelling to the midpoint instead of travelling 3.5km more.

Mei would have saved 10.5 minutes.



So, I drew an imaginary scenerio. If Lin had reached the end point of the race, and Mei did not stop moving, this is where they would both be at.



So in this scenerio, Mei has travelled two times of 3.5km more than she should.



So she wasted a total of 10.5 minutes x 2 = 21 minutes.



21 minutes after 10.45am is 11.06am.



Method at a glance.

3.5km ÷ 20 km/h = 10.5 minutes

10.5 minutes x 2 = 21 minutes

10.45am + 21 minutes = 11.06am