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

1. \(\frac15+\frac23=\frac3{15}+\frac{10}{15}=\frac{13}{15}\).
2. \(\frac56-\frac13=\frac56-\frac26=\frac12\).
3. \(\frac12\cdot\frac67=\frac37\).
4. \(\frac34:\frac15=\frac34\cdot5=\frac{15}{4}=3\frac34\).
5. \(2\frac14+1\frac56=\frac94+\frac{11}{6}=\frac{27}{12}+\frac{22}{12}=\frac{49}{12}=4\frac1{12}\).
6. \(4\frac34-\frac13=\frac{19}{4}-\frac13=\frac{57}{12}-\frac4{12}=\frac{53}{12}=4\frac5{12}\).
7. \(2\frac15\cdot3\frac49=\frac{11}{5}\cdot\frac{31}{9}=\frac{341}{45}=7\frac{26}{45}\).
8. \(4\frac12:1\frac23=\frac92:\frac53=\frac92\cdot\frac35=\frac{27}{10}=2\frac7{10}\).
9. \(\frac13+1=1\frac13\).
10. \(5-\frac25=4\frac35\).
11. \(10\cdot\frac25=4\).
12. \(\frac18:2=\frac18\cdot\frac12=\frac1{16}\).

Ответ: 1) 13/15; 2) 1/2; 3) 3/7; 4) 3 3/4; 5) 4 1/12; 6) 4 5/12; 7) 7 26/45; 8) 2 7/10; 9) 1 1/3; 10) 4 3/5; 11) 4; 12) 1/16.