Question

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

• A. $1$
• B. $14$
• C. $20$
• D. $21$

Answer 1

The correct option is C $20$

Clearly, the numbers which have $1$ or $9$ in the unit's digit, have square that end in the digit $1$. Such numbers from $1$ $70$ are $1,9,11,19,21,29,31,39,41,49,51,59,61,69$.
Number of such number $=14$
$\therefore$ Required percentage $=(\frac{14}{70}\times 100)$% $=20$%