🔢 Number Puzzles & Digits
Digit tricks, place value, and number codes
➕ Digit sums and divisibility
The digit sum is what you get when you add all the digits in a number. For example, 3742 has digit sum 3 + 7 + 4 + 2 = 16.
Divisibility rule: A number is divisible by 3 if its digit sum is divisible by 3. A number is divisible by 9 if its digit sum is divisible by 9. This is powerful for checking answers quickly!
Example:
Is 486 divisible by 9? Digit sum = 4 + 8 + 6 = 18. Is 18 divisible by 9? Yes! So 486 is divisible by 9. (486 ÷ 9 = 54 ✓)
🔄 Place value and rearranging digits
The number 3742 means 3×1000 + 7×100 + 4×10 + 2×1. Rearranging digits changes the number drastically!
To make the largest number: put the biggest digit first. To make the smallest: put the smallest non-zero digit first (not zero, because 0234 = 234).
Example: Using digits 5, 1, 3 — largest number is 531, smallest is 135 (not 315, because we want the smallest overall).
📝 Number codes and symbols
In competition problems, shapes often stand for unknown digits. Set up equations and solve step by step.
Example: If ★ + ★ + ★ = 12, then ★ = 4. Now if ★ + ● = 9, then 4 + ● = 9, so ● = 5. Solve the easiest equation first!
🧠 Practice Quiz
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