1. Вычисли: 5039 × 400; 780600 × 900; 215000 × 80.

\(5039 \times 400 = 5039 \times 4 \times 100 = 20156 \times 100 = 2\,015\,600\).

\(780600 \times 900 = 780600 \times 9 \times 100 = 7\,025\,400 \times 100 = 702\,540\,000\).

\(215000 \times 80 = 215000 \times 8 \times 10 = 1\,720\,000 \times 10 = 17\,200\,000\).

Ответ: 2 015 600; 702 540 000; 17 200 000.