780. a) 35 ⋅ 98 + 350 ⋅ 0,2; б) 29 ⋅ 25 + 2,9 ⋅ 50; в) 5,4 ⋅ 27 – 1,7 ⋅ 54; г) 37 ⋅ 34 + 3,4 ⋅ 630.

a) 35 ⋅ 98 + 350 ⋅ 0,2

\[35 \cdot 98 + 350 \cdot 0.2 = 3430 + 70 = 3500\]

б) 29 ⋅ 25 + 2,9 ⋅ 50

\[29 \cdot 25 + 2.9 \cdot 50 = 725 + 145 = 870\]

в) 5,4 ⋅ 27 – 1,7 ⋅ 54

\[5.4 \cdot 27 - 1.7 \cdot 54 = 145.8 - 91.8 = 54\]

г) 37 ⋅ 34 + 3,4 ⋅ 630

\[37 \cdot 34 + 3.4 \cdot 630 = 1258 + 2142 = 3400\]

Ответ: a) 3500; б) 870; в) 54; г) 3400