Square and Square Roots

Without adding find the sum
$$1+3+5+7+9+11+13+15+17+19$$
Find the square of the following number without multiplication.
Find the least number of four digits which is a perfect square.
Simplify $$\sqrt {6 \times \sqrt {6 \times \sqrt {6 \times \sqrt 6 .....\infty } } } $$
What could be the possible ones digits of the square root of each of the following numbers?
$$9801$$