I looked at online tutorials and im stuck at this case.
21/2
First, 2 goes into 2 once, so put 1 in the quotient, 2*1 = 2 so 2-2 = 0. Now we bring the 1 in 21 down. 2 doesnt go into 0, so what do we do in this case?
When i looked online, they went straight to saying 2 goes into 21 10 times so put 10 on the quotient, and 21-20= 1 is the remainder. But I was taught to divide the divsor by the divident one digit at a time.
$$ \require{enclose} \begin{array}{r} 10 \\[-3pt] 2 \enclose{longdiv}{21} \\[-3pt] \underline{2}\phantom{2} \\[-3pt] 1 \\[-3pt] \underline{0} \\1 \end{array} $$
Now that we found out the quotient is $10$ and the remainder is $1$, the relationship is $$21=2(10)+1$$
$$\frac{21}{2}=10+\frac12=10.5$$
As we learn more maths, we learn more tricks and we speed things up. It should be quite clear that $2(10)=20$ and $21-20=1$.