К-2: 503·38; 391·72; 820·26; 6084·63.

1. \(503\cdot38=503\cdot(30+8)=15\,090+4\,024=19\,114\).

2. \(391\cdot72=391\cdot(70+2)=27\,370+782=28\,152\).

3. \(820\cdot26=820\cdot(20+6)=16\,400+4\,920=21\,320\).

4. \(6084\cdot63=6084\cdot(60+3)=365\,040+18\,252=383\,292\).

Ответ: 19 114; 28 152; 21 320; 383 292.