The 'Ending in 5' Square Superpower!

Ever wish you could instantly square numbers like 35, 65, or even 105 in your head? Well, you can with this amazing trick!

Subject: mental-calculation • Classes: 6–12 • Difficulty: basic

The Trick

To square any number ending in 5 (let's call it $N5$): \n1. The last two digits of your answer will ALWAYS be $25$. \n2. Take the digit(s) before the 5 (let's call this $N$). Multiply $N$ by the next consecutive integer, which is $(N+1)$. \n3. Combine these two parts: the result from step 2, followed by $25$. \n\nWHY it works: For a number like $10N+5$, its square is $(10N+5)^2 = 100N^2 + 100N + 25 = 100N(N+1) + 25$. This means the $N(N+1)$ part is multiplied by 100 (so it comes before $25$).

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