Question

1/5+8/25+7/25; 1/7+2/21+3/7; 1/15+2/45+7/15; 3/49+5/7+4/49; 7/10+2/15+11/30; 1/12+1/18+1/12; решить дроби ,расписать как решали.

Answer 1

1)

$\tt\displaystyle \frac{1}{5}+\frac{8}{25}+\frac{7}{25}=\frac{1*5}{5*5}+\frac{8}{25}+\frac{7}{25}=\frac{5}{25}+\frac{8}{25}+\frac{7}{25}=\\\\\\=\frac{5+8+7}{25}=\frac{20}{25}=\frac{20:5}{25:5}=\frac{4}{5}=\frac{4*2}{5*2}=\frac{8}{10}=0,8$

2)

$\tt\displaystyle \frac{1}{7}+\frac{2}{21}+\frac{3}{7}=\frac{1*3}{7*3}+\frac{2}{21}+\frac{3*3}{7*3}=\frac{3}{21}+\frac{2}{21}+\frac{9}{21}=\\\\\\=\frac{3+2+9}{21}=\frac{14}{21}=\frac{14:7}{21:7}=\frac{2}{3}$

3)

$\tt\displaystyle \frac{1}{15}+\frac{2}{45}+\frac{7}{15}=\frac{1*3}{15*3}+\frac{2}{45}+\frac{7*3}{15*3}=\frac{3}{45}+\frac{2}{45}+\frac{21}{45}=\\\\\\=\frac{3+2+21}{45}=\frac{26}{45}$

4)

$\tt\displaystyle \frac{3}{49}+\frac{5}{7}+\frac{4}{49}=\frac{3}{49}+\frac{5*7}{7*7}+\frac{4}{49}=\frac{3}{49}+\frac{35}{49}+\frac{4}{49}=\\\\\\=\frac{3+35+4}{49}=\frac{42}{49}=\frac{42:7}{49:7}=\frac{6}{7}$

5)

$\tt\displaystyle \frac{7}{10}+\frac{2}{15}+\frac{11}{30}=\frac{7*3}{10*3}+\frac{2*2}{15*2}+\frac{11}{30}=\frac{21}{30}+\frac{4}{30}+\frac{11}{30}=\\\\\\=\frac{21+4+11}{30}=\frac{36}{30}=\frac{36:6}{30:6}=\frac{6}{5}=\frac{6*2}{5*2}=\frac{12}{10}=1,2$

6)

$\tt\displaystyle \frac{1}{12}+\frac{1}{18}+\frac{1}{12}=\frac{1*3}{12*3}+\frac{1*2}{18*2}+\frac{1*3}{12*3}=\frac{3}{36}+\frac{2}{36}+\frac{3}{36}=\\\\\\=\frac{3+2+3}{36}=\frac{8}{36}=\frac{8:4}{36:4}=\frac{2}{9}$