Use a calculator to find a percentage of an amount
Apply to real-life: discounts, tips, commission, interest
Real-World Applications
Finance: Calculating interest on savings accounts, commission earned on sales, and tax owed on income all require finding a percentage of an amount accurately.
Retail: Shop discounts and markups are expressed as percentages — finding the sale price or the profit margin on an item uses exactly this method.
Healthcare: Medication dosages are sometimes prescribed as a percentage of body weight, so nurses and pharmacists calculate a percentage of an amount to find the correct dose for each patient.
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With a calculator, the fastest method is to convert the percentage to a decimal, then multiply. The decimal version of a percentage is called the decimal multiplier.
\(\text{Percentage of amount} = \text{decimal} \times \text{amount}\)
Example 1: Find 35% of £240
Step 1
Convert 35% to a decimal: 35 ÷ 100 = 0.35
Step 2
Multiply: 0.35 × 240 = £84
Answer
£84
Example 2: Find 68% of £3500 (annual salary increase check)
Step 1
68% = 68 ÷ 100 = 0.68
Step 2
0.68 × 3500 = £2380
Answer
£2380
Example 3: Find 7.5% of £820
Step 1
7.5% = 7.5 ÷ 100 = 0.075
Step 2
0.075 × 820 = £61.50
Answer
£61.50
Tip — Converting % to decimal: Divide by 100. Move the decimal point 2 places to the left.
47% → 0.47 | 6% → 0.06 | 150% → 1.50
✓ Quick Check 1 — The Decimal Multiplier Method
Working backwards to find what percentage one number is of another gets its own full lesson — see Lesson 5.4 — Expressing One Number as a Percentage of Another.
Real-Life — Discounts, Tips, Commission, Interest
Percentages appear constantly in real life. Let's practise multi-step problems involving discounts, tips, commission, and simple interest.
Example 7: A television costs £450. It has a 15% discount. What is the sale price?
Step 1
Find 15% of £450: 0.15 × 450 = £67.50
Step 2
Sale price = £450 − £67.50 = £382.50
Example 8: A sales agent earns 8% commission on sales of £3,200. How much commission?
Step 1
Commission = 8% of £3,200
Step 2
0.08 × 3200 = £256
Example 9: A restaurant bill is £85. A 12% tip is added. What is the total?
Step 1
Tip = 12% of £85 = 0.12 × 85 = £10.20
Step 2
Total = £85 + £10.20 = £95.20
Watch out! Read carefully — does the question ask for the percentage amount (the discount or tip), or the final total after adding or subtracting?