Step 1 :
Divide $ 11891 $ by $ 2238 $ and get the remainder

$$ 11891 : 2238 = 5 \text{ ( remainder is } \color{blue}{ 701 } \text{ ) } $$

The remainder is positive ($ 701 > 0 $), so we will continue with division.

Step 2 :
Divide $ 2238 $ by $ \color{blue}{ 701 } $ and get the remainder

$$ 2238 : 701 = 3 \text{ ( remainder is } \color{blue}{ 135 } \text{ ) } $$

The remainder is still positive ($ 135 > 0 $), so we will continue with division.

Step 3 :
Divide $ 701 $ by $ \color{blue}{ 135 } $ and get the remainder

$$ 701 : 135 = 5 \text{ ( remainder is } \color{blue}{ 26 } \text{ ) } $$

The remainder is still positive ($ 26 > 0 $), so we will continue with division.

Step 4 :
Divide $ 135 $ by $ \color{blue}{ 26 } $ and get the remainder

$$ 135 : 26 = 5 \text{ ( remainder is } \color{blue}{ 5 } \text{ ) } $$

The remainder is still positive ($ 5 > 0 $), so we will continue with division.

Step 5 :
Divide $ 26 $ by $ \color{blue}{ 5 } $ and get the remainder

$$ 26 : 5 = 5 \text{ ( remainder is } \color{blue}{ 1 } \text{ ) } $$

The remainder is still positive ($ 1 > 0 $), so we will continue with division.

Step 6 :
Divide $ 5 $ by $ \color{blue}{ 1 } $ and get the remainder

$$ 5 : \color{blue}{ \boxed { 1 }} = 5 \text{ ( remainder is } \color{blue}{ 0 } \text{ ) } $$

The remainder is zero => GCD is the last divisor $ \color{blue}{ \boxed { 1 }} $.

This solution can be visualized using a Venn diagram.

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

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