$a){\left(-2\right)}^3\cdot 5^2=-8\cdot 25=-200$  

$b)2\cdot {\left(-0,1\right)}^2+{\left(\frac{5}{2}\right)}^{-3}=2\cdot 0,01+{\left(\frac{2}{5}\right)}^3=0,02+\frac{8}{125}=\frac{20}{1000}+\frac{64}{1000}=\frac{84}{1000}=0,084$