🔢 Mastering Percentages: From Shopping Deals to Interest Wheels

Ever wondered how discounts during a sale or the growth of money in a bank account are calculated? Percentages are everywhere! Understanding them is **crucial** for excelling in your O Level exams and making smart day-to-day decisions.

Main Concept: Percentage Change & Interest

A percentage is simply "per 100". To find a **percentage increase**, add the change to the original value; for a **percentage decrease**, subtract it. Simple interest grows linearly using

I = \frac{P r t}{100}

, while compound interest grows exponentially via

A = P\left(1+\frac{r}{100}\right)^n

Identify the **original amount** (100%).
Determine the **change** (increase or decrease).
Apply the **simple interest** formula when interest is added once per period without reinvesting.
Use the **compound interest** formula when interest is added to the principal, so future interest earns interest too.

Worked Example: Holiday Savings

Problem: You deposit

500

into an account that offers

4\%

compound interest per year. How much will you have after 3 years?

Step 1: Identify values: $P = 500$ , $r = 4$ , $n = 3$ .
Step 2: Apply
$A = P\left(1+\frac{r}{100}\right)^n = 500\left(1+\frac{4}{100}\right)^3$
.
Step 3: Evaluate:
$A = 500(1.04)^3 = 500 \times 1.124864 \approx 562.43$
.
Step 4: Therefore, after 3 years, you will have ** $\$ 562.43$**.

Practice regularly to make percentage problems second nature, and you will handle exam questions with confidence!