1. Let set $A=\{2,0,1,8\}, B=\{2 a \mid a \in A\}$, then the sum of all elements in $A \cup B$ is
Answer: 31.
Solution: It is easy to know that $B=\{4,0,2,16\}$, so $A \cup B=\{0,1,2,4,8,16\}$. The sum of all elements in $A \cup B$ is $0+1+2+4+8+16=31$.