5.1. Вычислите: a) $$\frac{729 \cdot 428 - 729 \cdot 311 + 117 \cdot 71}{320 \cdot 215 + 19 \cdot 320 - 120 \cdot 234}$$ б) $$5 + 2\frac{1}{3} : (-9,8) - 5 : (-21)$$

а)

1. $$729 \cdot 428 = 311952$$
2. $$729 \cdot 311 = 226719$$
3. $$117 \cdot 71 = 8307$$
4. $$311952 - 226719 = 85233$$
5. $$85233 + 8307 = 93540$$
6. $$320 \cdot 215 = 68800$$
7. $$19 \cdot 320 = 6080$$
8. $$120 \cdot 234 = 28080$$
9. $$68800 + 6080 = 74880$$
10. $$74880 - 28080 = 46800$$
11. $$\frac{93540}{46800} = \frac{9354}{4680} = \frac{4677}{2340} = \frac{1559}{780}$$

б)

1. $$5 + 2\frac{1}{3} = 5 + \frac{7}{3} = \frac{15+7}{3} = \frac{22}{3}$$
2. $$\frac{22}{3} : (-9,8) = \frac{22}{3} : (-\frac{98}{10}) = \frac{22}{3} \cdot (-\frac{10}{98}) = \frac{220}{294} = \frac{110}{147}$$
3. $$5 : (-21) = -\frac{5}{21}$$
4. $$\frac{110}{147} - (-\frac{5}{21}) = \frac{110}{147} + \frac{5}{21} = \frac{110}{147} + \frac{5 € € 7}{21 € € 7} = \frac{110+35}{147} = \frac{145}{147}$$
5. $$5 + \frac{145}{147} = \frac{5 € € 147}{147} + \frac{145}{147} = \frac{735+145}{147} = \frac{880}{147}$$

Ответ: а) $$\frac{1559}{780}$$, б) $$\frac{880}{147}$$.