Question

Find the square root of 2116.
___

Answer 1

Look at the unit digit - Unit digit of square is 6, so unit digit of square root will end in 4 or 6.
Ignore the last two digits and find the nearest number whose perfect square is less than or equal to the remaining number.
Here, $4^2$ = 16 is the nearest perfect square less than 21. So, ten’s digit is 4.
To find the unit digit, multiply the ten's digit with the next number (i.e. 4$\times$5).
If 21 is $\ge$ the product, then the unit digit is 6. If 21 is $<$ the product, then the unit digit is 4.
Here, 4 $\times$ 5 = 20 < 21. So, the square root of 2116 is 46.