1 вариант. Вычислите: 1) 1/4 + 2/5; 2) 5/7 − 1/2; 3) 1/3 · 6/10; 4) 3/5 : 1/5; 5) 2 3/4 + 1 5/6; 6) 4 1/4 − 2/3; 7) 1 1/2 · 3 4/9; 8) 4 1/6 : 1 2/3; 9) 1/2 + 2; 10) 3 − 2/5; 11) 5 · 2/5; 12) 7/8 : 7.

1. \(\frac14+\frac25=\frac5{20}+\frac8{20}=\frac{13}{20}\).
2. \(\frac57-\frac12=\frac{10}{14}-\frac7{14}=\frac3{14}\).
3. \(\frac13\cdot\frac6{10}=\frac6{30}=\frac15\).
4. \(\frac35:\frac15=\frac35\cdot5=3\).
5. \(2\frac34+1\frac56=\frac{11}{4}+\frac{11}{6}=\frac{33}{12}+\frac{22}{12}=\frac{55}{12}=4\frac7{12}\).
6. \(4\frac14-\frac23=\frac{17}{4}-\frac23=\frac{51}{12}-\frac8{12}=\frac{43}{12}=3\frac7{12}\).
7. \(1\frac12\cdot3\frac49=\frac32\cdot\frac{31}{9}=\frac{31}{6}=5\frac16\).
8. \(4\frac16:1\frac23=\frac{25}{6}:\frac53=\frac{25}{6}\cdot\frac35=\frac52=2\frac12\).
9. \(\frac12+2=2\frac12\).
10. \(3-\frac25=2\frac35\).
11. \(5\cdot\frac25=2\).
12. \(\frac78:7=\frac78\cdot\frac17=\frac18\).

Ответ: 1) 13/20; 2) 3/14; 3) 1/5; 4) 3; 5) 4 7/12; 6) 3 7/12; 7) 5 1/6; 8) 2 1/2; 9) 2 1/2; 10) 2 3/5; 11) 2; 12) 1/8.