Step 1 :
Divide $ 15990 $ by $ 10990 $ and get the remainder

$$ 15990 : 10990 = 1 \text{ ( remainder is } \color{blue}{ 5000 } \text{ ) } $$

The remainder is positive ($ 5000 > 0 $), so we will continue with division.

Step 2 :
Divide $ 10990 $ by $ \color{blue}{ 5000 } $ and get the remainder

$$ 10990 : 5000 = 2 \text{ ( remainder is } \color{blue}{ 990 } \text{ ) } $$

The remainder is still positive ($ 990 > 0 $), so we will continue with division.

Step 3 :
Divide $ 5000 $ by $ \color{blue}{ 990 } $ and get the remainder

$$ 5000 : 990 = 5 \text{ ( remainder is } \color{blue}{ 50 } \text{ ) } $$

The remainder is still positive ($ 50 > 0 $), so we will continue with division.

Step 4 :
Divide $ 990 $ by $ \color{blue}{ 50 } $ and get the remainder

$$ 990 : 50 = 19 \text{ ( remainder is } \color{blue}{ 40 } \text{ ) } $$

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

Step 5 :
Divide $ 50 $ by $ \color{blue}{ 40 } $ and get the remainder

$$ 50 : 40 = 1 \text{ ( remainder is } \color{blue}{ 10 } \text{ ) } $$

The remainder is still positive ($ 10 > 0 $), so we will continue with division.

Step 6 :
Divide $ 40 $ by $ \color{blue}{ 10 } $ and get the remainder

$$ 40 : \color{blue}{ \boxed { 10 }} = 4 \text{ ( remainder is } \color{blue}{ 0 } \text{ ) } $$

The remainder is zero => GCD is the last divisor $ \color{blue}{ \boxed { 10 }} $.

This solution can be visualized using a Venn diagram.

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

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