Question:
The number of boys and girls in a hall was in the ratio 4 : 5.
After 170 boys and 20% of the girls went back to their classrooms, the ratio of the number of boys to the number of girls in the hall became 1 : 2. How many children were there in the hall in the end?
Solution:
![P6 / Nan Hua / 2020 / SA2 Prelims / Paper 1 – Q10 [1 mark]](https://i0.wp.com/sgprimaths.com/wp-content/uploads/2022/02/P6_SA2_2020_Nan_Hua_Paper1_Q10-Qns.jpg?resize=400%2C260&ssl=1)
![P6 / ACS / 2019 / SA1 / Paper 2 – Q03 [2 marks]](https://i0.wp.com/sgprimaths.com/wp-content/uploads/2020/04/P6_ACS_2019_SA1_Paper2_Q03-Qns.jpg?resize=400%2C260&ssl=1)