Вычисли: 1) 64,283 + 18,977; 2) 1,2768 : 4,2; 3) 9/20 − 1/5; 4) 6 2/3 · 1,8; 5) −243 + 57; 6) −8,2 + (6 − 2 3/4) : 3/8.

1. \(64{,}283+18{,}977=83{,}26\).
2. \(1{,}2768:4{,}2=0{,}304\).
3. \(\frac{9}{20}-\frac{1}{5}=\frac{9}{20}-\frac{4}{20}=\frac{5}{20}=\frac{1}{4}\).
4. \(6\frac{2}{3}\cdot1{,}8=\frac{20}{3}\cdot\frac{9}{5}=12\).
5. \(-243+57=-186\).
6. \(-8{,}2+(6-2\frac{3}{4}):\frac{3}{8}=-8{,}2+\left(\frac{24}{4}-\frac{11}{4}\right)\cdot\frac{8}{3}=-8{,}2+\frac{13}{4}\cdot\frac{8}{3}=-8{,}2+\frac{26}{3}=\frac{64}{15}\).

Ответ: 1) 83,26; 2) 0,304; 3) 1/4; 4) 12; 5) −186; 6) 64/15.