$A, B, C$ are 3 prime numbers less than 20, $A+B+C=30$, find these three prime numbers $\qquad$
【Analysis and Solution】
Number Theory, Prime Numbers.
Since "odd number + odd number + odd number = odd number";
Therefore, among these three prime numbers, at least one is even, meaning these three prime numbers must include the even prime number 2; then the sum of the other two prime numbers is $30-2=28$;
Decompose 38 into the sum of two prime numbers: $28=5+23=11+17$;
Also, because $A, B, C$ are 3 prime numbers less than 20;
So the other two distinct prime numbers are $11, 17$;
Therefore, these three prime numbers are $2, 11, 17$.