Simplify these expressions $\sqrt{200a}+\sqrt{128a}-\sqrt{8a}$.The simplified form of expression is $\sqrt{2a}$

Without using a calculator, write down or estimate the square roots of the number :$121$.

Without using a calculator, write down or estimate the square roots of the number :$64$.

Without using a calculator, write down or estimate the square root of the number : 

$15$ 

(Answer in $3$ decimals).

Without using a calculator, write down or estimate the square root of the number :$12$. (Round off the answer up to $3$ decimal places).

Without using a calculator, write down or estimate the square roots of the number: $27$. (Round off the answer up to $3$ decimal places).

Without using a calculator, write down or estimate the square roots of the number :$50$ . (Answer in $3$ decimals).

Without using a calculator, estimate the value of the principal square roots. $\sqrt{24}$ . (Answer in $3$ decimals).

Without using a calculator, estimate the value of the principal square roots. $\sqrt{55}$. (Round off the answer up to $3$ decimal places).