Step 1 : Find prime factorization of each number.

$$\begin{aligned}3963 =& 3\cdot1321\\[8pt]6933 =& 3\cdot2311\\[8pt]9633 =& 3\cdot13\cdot13\cdot19\\[8pt]\end{aligned}$$

(view steps on how to factor 3963, 6933 and 9633. )

Step 2 : Put a box around factors that are common for all numbers:

$$\begin{aligned}3963 =& \color{blue}{\boxed{3}}\cdot1321\\[8pt]6933 =& \color{blue}{\boxed{3}}\cdot2311\\[8pt]9633 =& \color{blue}{\boxed{3}}\cdot13\cdot13\cdot19\\[8pt]\end{aligned}$$

Step 3 : Multiply the boxed numbers together:

$$ GCD = 3 $$

This solution can be visualized using a Venn diagram.

The GCD equals the product of the numbers at the intersection.

GCD Calculator