$2000kg=2\cdot 1000kg=2\cdot {10}^{3}kg=2\cdot {10}^3\cdot 1000g=2\cdot {10}^3\cdot {10}^{3}g=2\cdot {10}^{6}g=2\cdot {10}^6\cdot 1000mg=2\cdot {10}^6\cdot {10}^{3}mg=2\cdot {10}^{9}mg$