Add 1 to 100 in seconds — Maths trick for kids

The trick

Pairs — “1 + 2 + … + n = n × (n + 1) ÷ 2”

1. Pair the first and last numbers: each pair adds to n + 1.
2. Count the pairs — or multiply n × (n + 1) and halve it.
3. Odd numbers 1 + 3 + 5 + …: count them and multiply that count by itself.

Use it for: Adding long lists, counting handshakes or cricket balls in a series, and Olympiad puzzles.

Worked example: 1 + 2 + 3 + … + 100 = 5050

✏️ 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”.

🏁 Trick 8 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 ⭐ Young Genius Adder badge when you pass — and a certificate when you finish all 5 tricks of Part 2 · Number magic. You can still take the test without signing in.

🖨️ Sum of 1 to 100 Worksheet

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