G2.1 If the tens digit of $5^{5^{5}}$ is $a$, find the value of $a$.
$5^{5^{5}}=\cdots \cdots \cdot 125$, the tens digit $=a=2$
Remark Original question: If the tenth-place digit $\cdots \cdots$, this is the position of the first digit to the right of the decimal point.