3. Решите примеры: 3/4 × 8/9; 1 1/2 × 2/3; 7/8 × 4/21; 5/6 + 10/12; 2 1/4 + 3; 3 1/3 + 1 2/3.

1. \(\frac34\cdot\frac89=\frac{3\cdot8}{4\cdot9}=\frac23\).
2. \(1\frac12\cdot\frac23=\frac32\cdot\frac23=1\).
3. \(\frac78\cdot\frac4{21}=\frac{7\cdot4}{8\cdot21}=\frac16\).
4. \(\frac56+\frac{10}{12}=\frac56+\frac56=\frac{10}{6}=1\frac23\).
5. \(2\frac14+3=5\frac14\).
6. \(3\frac13+1\frac23=5\).

Ответ: \(\frac23;\ 1;\ \frac16;\ 1\frac23;\ 5\frac14;\ 5\).