Squaring Numbers Ending in 5 - FAST!

Ever wished you could calculate squares like $25^2$ or $65^2$ in a blink? Unlock the secret to squaring any number ending in 5 with lightning speed!

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

The Trick

To square a number ending in 5 (like $N5$), simply take the digit(s) before the 5 (let's call it $N$), multiply it by the next consecutive integer ($N+1$), and then append '25' to the result. \n\nWhy it works: Consider a number $(10N+5)$. Squaring it gives $(10N+5)^2 = (10N)^2 + 2(10N)(5) + 5^2 = 100N^2 + 100N + 25 = 100N(N+1) + 25$. This means we're multiplying $N(N+1)$ by 100 (which shifts it two places left) and then adding 25.

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.