Percentages in seconds — Speed Calculation

The fast method

Build from 10% — “10% is ÷ 10; halve it for 5%, double it for 20%”

1. 10%: divide by 10. 1%: divide by 100.
2. 5% = half of 10%, 20% = double 10%, 15% = 10% + 5%.
3. 50% = half, 25% = half of a half.

Use it for: Discounts and sale prices, marks in percent, tips and GST, and percentages in Class 7–10.

🧮 Check your own sums with the free Percentage calculator — it shows the working.

Worked example: 15% of 360 = 54

✏️ Practice

Work it out in your head or on paper, then tap your answer — or type it and press Check. Stuck? Press “Show me how”.

🏁 Lesson 12 test

20 questions. Check each answer, then go to the next one. Get 16 or more right to pass — and beat the clock: finish within 4 min.

🏅 Sign in with Google to earn the 📊 Percent Pilot badge when you pass — and a certificate when you finish all 5 lessons of Part 3 · Speed dividing, percentages and checking. You can still take the test without signing in.

🖨️ Percentage Worksheet – Mental Maths

• Worksheet set 1 (PDF)
• Worksheet set 2 (PDF)
• Worksheet set 3 (PDF)