The GCD of given numbers is 13.
Step 1 : Find prime factorization of each number.
$$\begin{aligned}1261 =& 13\cdot97\\[8pt]611 =& 13\cdot47\\[8pt]\end{aligned}$$(view steps on how to factor 1261 and 611. )
Step 2 : Put a box around factors that are common for all numbers:
$$\begin{aligned}1261 =& \color{blue}{\boxed{13}}\cdot97\\[8pt]611 =& \color{blue}{\boxed{13}}\cdot47\\[8pt]\end{aligned}$$Step 3 : Multiply the boxed numbers together:
$$ GCD = 13 $$This solution can be visualized using a Venn diagram.
The GCD equals the product of the numbers at the intersection.