Add and take away 9, 19 and 99 — Mental Maths Mastery

How to do it in your head

Round and adjust — “use the round number, then fix the 1”

1. Add 9, 19, 99: add 10, 20, 100, then take 1 away.
2. Take away 9, 19, 99: take away 10, 20, 100, then add 1 back.
3. Ask yourself: did I use too much or too little?

Use it for: Prices like ₹99 and ₹199, and any sum with a 9 at the end.

Worked example: 46 + 19 = 65

✏️ Practice

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

🏁 Lesson 4 test

20 questions. Check each answer, then go to the next one. Get 16 or more right to pass.

🏅 Sign in with Google to earn the 🎯 Nine Ninja badge when you pass — and a certificate when you finish all 7 lessons of Part 1 · Mental addition & subtraction. You can still take the test without signing in.

🖨️ Adding 9, 19 and 99 Mental Maths Worksheet

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