Number problems — Quantitative aptitude for kids

The method

Use the structure — “consecutive numbers share a middle; sum and difference give both numbers; swapping digits changes by 9 × the gap”

1. n consecutive numbers with sum S: the middle (average) is S ÷ n.
2. From sum and difference: larger = (sum + difference) ÷ 2, smaller = (sum − difference) ÷ 2.
3. Swapping the digits changes the number by 9 × (difference of the digits).
4. “k times another, difference D”: smaller = D ÷ (k − 1).

Use it for: Number puzzles in aptitude, Olympiad and scholarship tests, and early algebra.

Worked example: The digits of a two-digit number add up to 11. When the digits swap places, the number goes up by 27. What is the number? → 47

✏️ 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 27 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 🔢 Number Puzzler badge when you pass — and a certificate when you finish all 10 lessons of Part 3 · Aptitude challenge. You can still take the test without signing in.

🖨️ Number Problems Worksheet

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