Question

Find square root of $961$ using Vilokanam method.

• A. $29$
• B. $30$
• C. $31$
• D. $32$

Answer 1

Answer: (C)

$31$

We have to find the square root of $961$ using Vilokanam method.

Its unit digit is $1$.

Therefore, the unit digit of the square root will be $1$ or $9$.

Ignoring the last two digits (unit digit and ten’s digit) we get $9$.

The greatest number whose square is less than or equal to $9$ is $3$.

Adjusting above obtained two unit digits $1$ or $9$ to the right of $2$, we get two numbers $31$ and $39$.

The unique number with unit digit $5$ which lies between $31$ and $39$ is $35$.

And $(35{)}^2=1225$

Since, $961<1225$, therefore, the required square root is $31$.

Thus $\sqrt{961}=31$