This blog is managed by Song Hock Chye, author of Improve Your Thinking Skills in Maths (P1-P3 series), which is published and distributed by EPH.

## Monday, January 21, 2008

### MGS (Paya Lebar) Pri School P6 Math CA1 2006 (Q43)

Last year, the ratio of the number of boys to the number of girls in a chess club was 5 : 3. After 5 boys and 9 girls joined the club this year, the ratio became 5 : 4. How many girls were there in the chess club at first?

Solution

20 units + 20 ----- 15 units + 45
20 units – 15 units ----- 45 – 20
5 units ----- 25
1 unit ----- 25 divided by 5 = 5

(Girls at first) 3 units ----- 5 x 3 = 15

Answer: There were 15 girls at first.

Anonymous said...

Mr Song
Wish to seek your opinion on the use of equivalent ratio to solve this problem. This method may be more suitable for weaker students , but it’s longer
Before After
B:G B:G
5:3 5:4
25:15 30:24

As there is an increase of 5 boys and 9 girls
30-25 =5 boys
24-15 =9 girls
At first there are 15 girls
Will students be penalised if they use this method.

Excel Eduservice said...

Dear Anonymous,