47 Let $[A]$ denote the greatest integer less than or equal to $A$. Suppose $A=50+19 \sqrt{7}$, then $A^{2}-A[A]=$
47 27. $A=50+19 \sqrt{7}=(\sqrt{7}+2)^{3}$. Let $B=(\sqrt{7}-2)^{3}$, then $A-B=100$, that is, $A=100+B$. It is also easy to know that $0<B=(\sqrt{7}-2)^{3}<1$, so $[A]=100, A-[A]=$ B. Therefore, we have
$$
A^{2}-A[A]=A(A-[A])=A B=3^{3}=27 \text {. }
$$