$\text{a)}2000\cdot 123,45\cdot {10}^{11}=2\cdot \underline{{10}^3}\cdot 123,45\cdot \underline{{10}^{11}}=2\cdot 123,45\cdot {10}^{14}=$

$=246,9\cdot {10}^{14}=2,469\cdot {10}^2\cdot {10}^{14}=2,469\cdot {10}^{16}$  


$\text{b)}189,21\cdot {10}^{13}:300=\frac{189,21\cdot {10}^{13}}{300}=\frac{189,21\cdot {10}^{13}}{3\cdot {10}^2}=\frac{189,21}{3}\cdot \frac{{10}^{13}}{{10}^2}=$   

$=63,07\cdot {10}^{11}=6,307\cdot 10\cdot {10}^{11}=6,307\cdot {10}^{12}$  



Odpowiedź:  a) 2,469 · 10¹⁶,  b) 6,307 · 10¹²