**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.

Answer: There were 15 girls at first.

## 2 comments:

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.

Dear Anonymous,

My reply can be found in this link.

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