4. После сокращения дробей приведите их к данному знаменателю: a) 15 20 = 28 16 б) 40 = 45 48 B) 72 300 21 = 36 81 28 35 = 6 105

a)

1. $$\frac{15}{20} = \frac{15 \div 5}{20 \div 5} = \frac{3}{4}$$
2. $$\frac{3}{4} = \frac{3 \cdot 7}{4 \cdot 7} = \frac{21}{28}$$
3. $$\frac{21}{28} = \frac{21 \div 7}{28 \div 7} = \frac{3}{4}$$
4. $$\frac{3}{4} = \frac{3 \cdot 9}{4 \cdot 9} = \frac{27}{36}$$
5. Ответ: $$\frac{21}{28}$$, $$\frac{27}{36}$$

б)

1. $$\frac{16}{40} = \frac{16 \div 8}{40 \div 8} = \frac{2}{5}$$
2. $$\frac{2}{5} = \frac{2 \cdot 9}{5 \cdot 9} = \frac{18}{45}$$
3. $$\frac{28}{36} = \frac{28 \div 4}{36 \div 4} = \frac{7}{9}$$
4. $$\frac{7}{9} = \frac{7 \cdot 9}{9 \cdot 9} = \frac{63}{81}$$
5. Ответ: $$\frac{18}{45}$$, $$\frac{63}{81}$$

в)

1. $$\frac{48}{72} = \frac{48 \div 24}{72 \div 24} = \frac{2}{3}$$
2. $$\frac{2}{3} = \frac{2 \cdot 100}{3 \cdot 100} = \frac{200}{300}$$
3. $$\frac{35}{105} = \frac{35 \div 35}{105 \div 35} = \frac{1}{3}$$
4. $$\frac{1}{3} = \frac{1 \cdot 2}{3 \cdot 2} = \frac{2}{6}$$
5. Ответ: $$\frac{200}{300}$$, $$\frac{2}{6}$$