3. If $x, y, z, t \in \mathbf{N}_{+}$, and $1 \leqslant x<y \leqslant z$ $<t \leqslant 100$, then the maximum and minimum values of $\frac{x}{y}+\frac{z}{t}$ are $\qquad$.
3. $\frac{19601}{9900}, \frac{1}{5}$.

It is easy to know, $\frac{x}{y}+\frac{z}{t} \leqslant \frac{98}{99}+\frac{99}{100}=\frac{19601}{9900}$.
$$
\text { Also, } \frac{x}{y}+\frac{z}{t} \geqslant \frac{1}{y}+\frac{z}{100} \geqslant 2 \sqrt{\frac{z}{100 y}} \geqslant \frac{1}{5} \text {. }
$$

Equality in (1) holds if and only if $\frac{1}{y}=\frac{z}{100}, y=z, x=1, t=100$, i.e., $x=$ $1, y=z=10, t=100$.