⚡️Fast Square Five!⚡️

Ever wonder if there's a lightning-fast way to square ANY number ending in 5 without a calculator? Get ready to amaze yourself!

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

The Trick

To square any number that ends in 5 (e.g., $N5$), follow these two simple steps: 1. The last two digits of your answer will ALWAYS be $\mathbf{25}$. 2. Take the digit(s) before the 5 (let's call it $N$). Multiply $N$ by the next consecutive integer, $(N+1)$. Combine the result from step 2 with the '25' from step 1. That's your answer! **Why it works:** Let the number be $(10N + 5)$. Squaring it gives $(10N + 5)^2 = (10N)^2 + 2(10N)(5) + 5^2 = 100N^2 + 100N + 25 = 100N(N+1) + 25$. This shows $N(N+1)$ is multiplied by 100 (shifting it to the left) and then 25 is added.

Study More with GyanAI

GyanAI is a free AI tutor for CBSE students. Ask any question for an instant step-by-step answer. Try GyanAI free.