DSE 數學公式 (Maths Formula): Percentage 百分比公式公式

Percentage Formula

• Percentage change:\frac{New  value−Old  value}{Old  value} × 100%

↳ Percentage increase / decrease: 答案要正數

• Increase / Decrease: New value = Old  value × (1 ± \begin{array}{c} Increase\% \\ Decrease\% \end{array} )

🌟容易搞亂乘除的同學，建議一律由舊值開始用「乘」，不知舊值則設x

• Profit / Loss / Discount

Profit / Loss：Cost × (1 ± \begin{array}{c} Profit\% \\ Loss\% \end{array} ) = Selling price

🌟一條式可以搵三樣野(Cost / % / SP)，邊個唔知就設未知數

🌟容易搞亂乘除的同學，建議一律由成本開始用「乘」，不知成本則設x

Selling price – cost = Profit (Loss)

Discount：Marked price (1 – Discount %) = Selling price

                     Marked price – selling price = Discount

• Interest

Simple Interest: A = P (1 + r% ×  T)  

Compound interest:A = P × (1 + \frac{r\%}{n})^ {Tn}

Interest = A – P 

[A = Amount, P = Principal, r = rate per annum, 

T = Number of years, n = Number of periods in a year]

Remark: 

Compounded monthly: n = 12

Compounded half-yearly: n = 2

Compounded quarterly: n = 4

百分比公式

• 百分變化： \frac{新值 - 舊值}{舊值} × 100%

↳ 百分上升 / 下降: 答案要正數

• 上升 / 下降： 新值 = 舊值 × （1 ± \begin{array}{c} 上升\% \\ 下降\% \end{array} )

🌟容易搞亂乘除的同學，建議一律由舊值開始用「乘」，不知舊值則設x

• 盈利 / 虧蝕 / 折扣

盈利 / 虧蝕：成本 × (1 ±  \begin{array}{c} 盈利\% \\ 虧蝕\% \end{array} ) = 售價

🌟一條式可以搵三樣野(Cost / % / SP)，邊個唔知就設未知數

🌟容易搞亂乘除的同學，建議一律由成本開始用「乘」，不知成本則設x

售會 – 成本 = 盈利 (虧蝕)

折扣：標價 (1 – 折扣 %) = 售價

             標價 – 售價 = 折扣

• 利息

單利息：A = P (1 + r% ×  T)  

複利息：A = P × (1 + \frac{r\%}{n}) ^{Tn}

利息= A – P 

[A = 本利和, P = 本金, r = 年利率, 

T = 時期, n = 每年期數]

Remark: 

每月一結: n = 12

每半年一結: n = 2

每季一結: n = 4