12 bags contain 8 white balls and 2 red balls. Each time, one ball is randomly taken out, and then 1 white ball is put back. The probability that exactly all red balls are taken out by the 4th draw is $\qquad$ .
Solve for the probability that all red balls are taken out exactly on the 4th draw:
$$
\begin{aligned}
& \frac{2}{10} \times\left(\frac{9}{10}\right)^{2} \times \frac{1}{10}+\frac{8}{10} \times \frac{2}{10} \times \frac{9}{10} \times \frac{1}{10}+\left(\frac{8}{10}\right)^{2} \times \frac{2}{10} \times \frac{1}{10} \\
= & 0.0434 .
\end{aligned}
$$