Question

How do find the square of a number ending with $5$?

Answer 1

Find the required number:

Let number be $\mathrm{x}5$

Then square of it is $\left[\mathrm{x}(\mathrm{x}+1)\right]\left[5^2\right]$

Example: $45$

$$\begin{gathered} {45}^2=\left[4(4+1)\right]\left[5^2\right] \\ {45}^2=\left[4\times 5\right]\left[25\right] \\ {45}^2=\left[20\right]\left[25\right] \\ {45}^2=2025 \end{gathered}$$

Therefore square of a number ending with $5$ is given by $\left[\mathrm{x}(\mathrm{x}+1)\right]\left[5^2\right]$.