Question

What percentage of numbers from $1$ to $70$ have $1$ or $9$ in the unit's digit?

Answer 1

Convert into percentage.

All numbers from $1$ to $70$ which have the unit digit $1$ or $9$ are,

$\{1,9,11,19,21,29,31,39,41,49,51,59,61,69\}=14\mathrm{numbers}$

And from $1$ to $70$ , there are $70$ numbers.

$\begin{array}{rcl}\mathrm{Required}\mathrm{percentage}& =& \frac{14}{70}\times 100\\ & =& \frac{1}{5}\times 100\\ & =& 20\%\end{array}$

Hence, the required percentage is $20\%$.