PSLE 2009 MATHEMATICS QUESTION

Jim bought some chocolates and gave half of it to Ken. Ken bought some sweets and gave half of it to Jim. Jim ate 12 sweets and Ken ate 18 chocolates.

The ratio of Jim's sweets to chocolates became 1 : 7 and the ratio of Ken's sweets to chocolates became 1:4. How many sweets did Ken buy?

Solution:

I started off with a model on Jim's ratio.



Since Jim ate 12 sweets, I added it in.



Then I drew Ken's ratio separately below. Take note that 1 unit of Ken is equals to 1 unit of Jim's sweet + 12 because Ken gave half of his sweet to Jim.



I drew the dotted red line to show the link.



Since Ken ate 18 chocolates, I added that in next.



So I cut every Ken's unit so that it is comparable to Jim's unit.



This is the tricky part. For each unit of Jim's chocolate, I cross out each white unit of Ken's chocolate.



So that leaves us with 3 units of Chocolate for Jim.



Those 3 units are actually made up of 12, 12, 12, 12 and 18.



So,



To find Ken's share of sweets,





Then I multiply by 2.



And there you have it. Ken had 68 sweets at first.

Isn't this way easier to explain to primary students, rather than using Simultaneous equations? Let me know what you think.

Method at a glance.

3 units --> 12 + 12 + 12 + 12 + 18
= 66

1 units --> 66 /3
= 22

22 + 12 = 34

34 x 2 = 68