Find the smallest $4$-digit number that is exactly divisible by 33

The sum of all the whole numbers from $15$ to $30$ can be found out by:

$\frac{\left(30+15\right)(30-15+1)}{2}$. Using this, find the sum of all the whole numbers from $21$ to$51$.

If $x,y$ and $z$ are three whole numbers then $x\times \left(y+z\right)=x\times y+x\times z$ will always be a whole number.

If $\mathrm{x},\mathrm{y}$  and  $z$  are two whole numbers then $\mathrm{x}\times \left(\mathrm{y}+\mathrm{z}\right)=\mathrm{x}\times \mathrm{y}+\mathrm{x}\times \mathrm{z}$ will always be a whole number.

If $x,y$ and $z$ are whole numbers, then $x+y=y+z\Rightarrow x=z$.

If $\mathrm{x},\mathrm{y}$  and  $z$  are  whole numbers then $\mathrm{x}-\mathrm{y}-\mathrm{z}\ne \mathrm{x}-(\mathrm{y}-\mathrm{z})$ where, $\mathrm{x}, \mathrm{y}, \mathrm{z}>0$

If $\mathrm{x}$ is a whole number then  $x÷x=1$, except when $\mathrm{x}=0$