1. For what value of $b$ do the equations $1988 x^{2}+b x+8891=0$,
and $\quad 8891 x^{2}+b x+1988=0$ have a common root?
1. If the two equations have a common root $x$, then we have
$$
1988 x^{2}+8891=8891 x^{2}+1988 .
$$

This is a quadratic equation, and it is evident that $x=1$ or -1. When $x=1$, we can determine
$$
b=-10879,
$$

When $x=-1$, $b=10879$.