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How can you square a number ending in 5 mentally?
Updated: 11-Apr-2025

For numbers ending in 5, like 25, multiply the first digit(s) by the next higher number, then append 25. For example, 25²: 2 × 3 = 6, then write 625. It works because (10n + 5)² = 100n(n + 1) + 25. It’s fast and reliable for numbers like 15, 25, 35, etc.

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