Step 1 :
Divide $ 860 $ by $ 240 $ and get the remainder

$$ 860 : 240 = 3 \text{ ( remainder is } \color{blue}{ 140 } \text{ ) } $$

The remainder is positive ($ 140 > 0 $), so we will continue with division.

Step 2 :
Divide $ 240 $ by $ \color{blue}{ 140 } $ and get the remainder

$$ 240 : 140 = 1 \text{ ( remainder is } \color{blue}{ 100 } \text{ ) } $$

The remainder is still positive ($ 100 > 0 $), so we will continue with division.

Step 3 :
Divide $ 140 $ by $ \color{blue}{ 100 } $ and get the remainder

$$ 140 : 100 = 1 \text{ ( remainder is } \color{blue}{ 40 } \text{ ) } $$

The remainder is still positive ($ 40 > 0 $), so we will continue with division.

Step 4 :
Divide $ 100 $ by $ \color{blue}{ 40 } $ and get the remainder

$$ 100 : 40 = 2 \text{ ( remainder is } \color{blue}{ 20 } \text{ ) } $$

The remainder is still positive ($ 20 > 0 $), so we will continue with division.

Step 5 :
Divide $ 40 $ by $ \color{blue}{ 20 } $ and get the remainder

$$ 40 : \color{blue}{ \boxed { 20 }} = 2 \text{ ( remainder is } \color{blue}{ 0 } \text{ ) } $$

The remainder is zero => GCD is the last divisor $ \color{blue}{ \boxed { 20 }} $.

This solution can be visualized using a Venn diagram.

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

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