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## Friday, February 19, 2010

### Nanyang Pri Sch 2009 P6 CA1 Math Paper 2 Q16

The ratio of the number of boys to the number of girls in School A is 4:1. the ratio of the number of boys to the number of girls in School B is 2:3. School A had twice as many pupils as School B.

a) What is the ratio of boys in School A to the number of girls in School B?

b) After 30 girls left School A to join School B, the ratio of the number of boys to the number of girls in School B is now 5:8. How many girls are there in School B now?

Solution

* School A is multiplied by 2 to give a total of 10 units. This is because School B has 5 units. School A has twice the number of pupils as School B.

(a)
Boys from School A --> 8 units
Girls from School B --> 3 units

Ratio of number of boys in School A to number of girls in School B
--> 8 : 3

b)
School B

* Before is multiplied by 5 and After is multiplied by 2 to make the boys have a common unit of 10 for both Before and After, because there was no transfer of boys.

Girls increased by 1 unit after the transfer
1 unit--> 30

Number of girls in School B after transfer
16 units --> 16 x 30 = 480