Question:
Mr Lee spent a total of $28.50 on some files, rulers and highlighters. He bought twice as many highlighters as files. Each ruler cost $0.50 and each file cost thrice as much as each highlighter. He spent $4.50 more on the files than on the highlighters. How many rulers did he buy?
Solution:
![P6 / Ai Tong / 2020 / SA2 Prelims / Paper 1 – Q16 [1 mark]](https://i0.wp.com/sgprimaths.com/wp-content/uploads/2021/08/P6_SA2_2020_Ai_Tong_Paper1_Q16-Qns.jpg?resize=400%2C142&ssl=1)
![P6 / Catholic High / 2020 / SA2 Prelims / Paper 1 – Q22 [2 marks]](https://i0.wp.com/sgprimaths.com/wp-content/uploads/2021/06/P6_SA2_2020_Catholic_High_Paper1_Q22-Qns.jpg?resize=400%2C260&ssl=1)
Hi mam/sir,
How comes the number 5 to be multiplied with 4.50?
From the last model on the right, we inferred that 1 unit = $4.50, and 5 units = highlighters + files = 5 x $4.50 = $22.50.
Hope this helps!
why is $4.50 1 unit
Hi! To understand why $4.50 = 1 unit, we need to understand all 3 models.
LEFT – Number of items
MIDDLE – Cost of 1 item
RIGHT – use LEFT x MIDDLE = Cost of all items bought
Therefore, we deduce that F = 3 units, H = 2 units, and the difference between them = $4.50. –> 1 unit = $4.50
Hope this clarifies!