10) (0,4)⁹x(0,4)¹⁸ (0,4)²¹x(0,4)²

$$\frac{(0.4)^9 \times (0.4)^{18}}{(0.4)^{21} \times (0.4)^2} = \frac{(0.4)^{9+18}}{(0.4)^{21+2}} = \frac{(0.4)^{27}}{(0.4)^{23}} = (0.4)^{27-23} = (0.4)^4 = 0.0256$$

Ответ: 0.0256