Find Greatest Common Divisor of 840 and 1080, using prime factorization.

Step 1 : Find prime factorization of each number.

$$\begin{aligned}840 =& 2\cdot2\cdot2\cdot3\cdot5\cdot7\\[8pt]1080 =& 2\cdot2\cdot2\cdot3\cdot3\cdot3\cdot5\\[8pt]\end{aligned}$$

(view steps on how to factor 840 and 1080. )

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

$$\begin{aligned}840 =& \color{blue}{\boxed{2}}\cdot\color{red}{\boxed{2}}\cdot\color{Fuchsia}{\boxed{2}}\cdot\color{Orange}{\boxed{3}}\cdot\color{Purple}{\boxed{5}}\cdot7\\[8pt]1080 =& \color{blue}{\boxed{2}}\cdot\color{red}{\boxed{2}}\cdot\color{Fuchsia}{\boxed{2}}\cdot\color{Orange}{\boxed{3}}\cdot3\cdot3\cdot\color{Purple}{\boxed{5}}\\[8pt]\end{aligned}$$

Step 3 : Multiply the boxed numbers together:

$$ GCD = 2\cdot2\cdot2\cdot3\cdot5 = 120 $$

This solution can be visualized using a Venn diagram.

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

GCD Calculator