Step 1 : Find prime factorization of each number.

$$\begin{aligned}210 =& 2\cdot3\cdot5\cdot7\\[8pt]2730 =& 2\cdot3\cdot5\cdot7\cdot13\\[8pt]\end{aligned}$$

(view steps on how to factor 210 and 2730. )

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

$$\begin{aligned}210 =& \color{blue}{\boxed{2}}\cdot\color{red}{\boxed{3}}\cdot\color{Fuchsia}{\boxed{5}}\cdot\color{Orange}{\boxed{7}}\\[8pt]2730 =& \color{blue}{\boxed{2}}\cdot\color{red}{\boxed{3}}\cdot\color{Fuchsia}{\boxed{5}}\cdot\color{Orange}{\boxed{7}}\cdot13\\[8pt]\end{aligned}$$

Step 3 : Multiply the boxed numbers together:

$$ GCD = 2\cdot3\cdot5\cdot7 = 210 $$

This solution can be visualized using a Venn diagram.

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

GCD Calculator