1. $[x]$ represents the greatest integer not exceeding the real number $x$. Suppose the real number $x$ is not an integer, and $x+\frac{99}{x}=[x]+\frac{99}{[x]}$. Then, the value of $x$ is
Ni.1. -9.9 .
Let $x=[x]+t, 0<t<1$.
Substitute into the equation (note $t \neq 0$ )
$$
t=\frac{99-[x]^{2}}{[x]}, [x] \in \mathbf{Z} \text {. }
$$

From $0<t<1$ we know $[x]=-10$.
Thus, $t=0.1, x=-9.9$.