The GCD of given numbers is 21.
Step 1 :
Divide $ 861 $ by $ 210 $ and get the remainder
The remainder is positive ($ 21 > 0 $), so we will continue with division.
Step 2 :
Divide $ 210 $ by $ \color{blue}{ 21 } $ and get the remainder
The remainder is zero => GCD is the last divisor $ \color{blue}{ \boxed { 21 }} $.
We can summarize an algorithm into a following table.
861 | : | 210 | = | 4 | remainder ( 21 ) | ||
210 | : | 21 | = | 10 | remainder ( 0 ) | ||
GCD = 21 |
This solution can be visualized using a Venn diagram.
The GCD equals the product of the numbers at the intersection.