四、生活中的数学。
1. 一本书共116页，小华已经看了86页，他已经看的页数是全书的几分之几？没有看的页数是全书的几分之几？

1. $86 ÷ 116 = \frac{43}{58}$ $1 - \frac{43}{58} = \frac{15}{58}$

2. 某工程队第一天铺路$\frac{8}{9}\ \mathrm{km}$，第二天铺路$\frac{4}{5}\ \mathrm{km}$，第三天铺的路比前两天铺的总长少$\frac{7}{9}\ \mathrm{km}$，第三天铺路多少千米？

2. $\frac{8}{9} + \frac{4}{5} - \frac{7}{9} = \frac{41}{45}(\mathrm{km})$

3. 学校运来一批石子,砌花坛用去$\frac{1}{8}$ t,修路用去$\frac{3}{5}$ t,还剩$\frac{1}{6}$ t,这批石子原有多少吨?

3. $\frac{1}{8} + \frac{3}{5} + \frac{1}{6} = \frac{107}{120}(\mathrm{t})$

4. 有一块布料,做上衣用去$\frac{7}{8}$ m,做裤子用去$\frac{3}{4}$ m,还剩$\frac{1}{12}$ m,这块布料一共有多少米?

4. $\frac{7}{8} + \frac{3}{4} + \frac{1}{12} = \frac{41}{24}(\mathrm{m})$

算一算
$\frac{3}{10} + \frac{9}{10} =$
$\frac{13}{18} + \frac{11}{18} =$
$\frac{5}{6} + \frac{7}{24} =$
$\frac{1}{6} + \frac{5}{12} =$
$\frac{3}{5} + \frac{6}{25} =$
$\frac{3}{5} + \frac{6}{15} =$
$\frac{3}{7} + \frac{11}{28} =$
$\frac{13}{24} + \frac{11}{24} =$
$\frac{18}{19} + \frac{11}{19} =$
$\frac{19}{27} + \frac{19}{27} =$

$\frac{3}{10} + \frac{9}{10} = \frac{3+9}{10} = \frac{12}{10} = \frac{6}{5}$
$\frac{13}{18} + \frac{11}{18} = \frac{13+11}{18} = \frac{24}{18} = \frac{4}{3}$
$\frac{5}{6} + \frac{7}{24} = \frac{20}{24} + \frac{7}{24} = \frac{27}{24} = \frac{9}{8}$
$\frac{1}{6} + \frac{5}{12} = \frac{2}{12} + \frac{5}{12} = \frac{7}{12}$
$\frac{3}{5} + \frac{6}{25} = \frac{15}{25} + \frac{6}{25} = \frac{21}{25}$
$\frac{3}{5} + \frac{6}{15} = \frac{3}{5} + \frac{2}{5} = \frac{5}{5} = 1$
$\frac{3}{7} + \frac{11}{28} = \frac{12}{28} + \frac{11}{28} = \frac{23}{28}$
$\frac{13}{24} + \frac{11}{24} = \frac{24}{24} = 1$
$\frac{18}{19} + \frac{11}{19} = \frac{29}{19}$
$\frac{19}{27} + \frac{19}{27} = \frac{38}{27}$