What percentage of the numbers from 1 to 50 have squares that end in the digit 1 ?

Answer: Option E

The squares of numbers having 1 and 9 as the unit's digit end in the digit 1.
$$\begin{array}{rl}& \text{Such numbers are,}\\ & 1,9,11,19,21,29,31,39,41,49\text{ i}\text{.e}\text{.,}\\ & \text{There are 10 such numbers}\text{.}\\ & \therefore \text{Required percentage}\\ & =\left(\frac{10}{50}\times 100\right)\%\\ & =20\%\end{array}$$