The GCD of given numbers is 10.
Step 1 :
Divide $ 30 $ by $ 10 $ and get the remainder
The remainder is zero => GCD is the last divisor $ \color{blue}{ \boxed { 10 }} $.
We can summarize an algorithm into a following table.
| 30 | : | 10 | = | 3 | remainder ( 0 ) |
| GCD = 10 | |||||
This solution can be visualized using a Venn diagram.
The GCD equals the product of the numbers at the intersection.