1. A bag contains 8 white balls and 2 red balls. Each time a ball is randomly drawn from the bag, and then a white ball is put back. What is the probability that all red balls are exactly drawn by the fourth draw?
$$
-1.0 .0434
$$

The probability of exactly taking all the red balls on the fourth draw is
$$
\begin{array}{l}
\frac{2}{10} \times\left(\frac{9}{10}\right)^{2} \times \frac{1}{10}+\frac{8}{10} \times \frac{2}{10} \times \frac{9}{10} \times \frac{1}{10}+\left(\frac{8}{10}\right)^{2} \times \frac{2}{10} \times \frac{1}{10} \\
=0.0434
\end{array}
$$