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(1)
$ \frac{1}{2} + \frac{3}{8} = \frac{(\ \ \ \ \ \ )}{(\ \ \ \ \ \ )} + \frac{(\ \ \ \ \ \ )}{(\ \ \ \ \ \ )} = \frac{(\ \ \ \ \ \ )}{(\ \ \ \ \ \ )} $
$ \frac{1}{2} + \frac{3}{8} = \frac{(\ \ \ \ \ \ )}{(\ \ \ \ \ \ )} + \frac{(\ \ \ \ \ \ )}{(\ \ \ \ \ \ )} = \frac{(\ \ \ \ \ \ )}{(\ \ \ \ \ \ )} $
答案
1. (1)
$\frac{4}{8}$ $\frac{3}{8}$ $\frac{7}{8}$(2)
$ \frac{1}{2} - \frac{1}{3} = \frac{(\ \ \ \ \ \ )}{(\ \ \ \ \ \ )} - \frac{(\ \ \ \ \ \ )}{(\ \ \ \ \ \ )} = \frac{(\ \ \ \ \ \ )}{(\ \ \ \ \ \ )} $
$ \frac{1}{2} - \frac{1}{3} = \frac{(\ \ \ \ \ \ )}{(\ \ \ \ \ \ )} - \frac{(\ \ \ \ \ \ )}{(\ \ \ \ \ \ )} = \frac{(\ \ \ \ \ \ )}{(\ \ \ \ \ \ )} $
答案
1. (2) $\frac{3}{6}$ $\frac{2}{6}$ $\frac{1}{6}$
在括号里填合适的数。
$\frac{3}{4}+\frac{5}{3}=\frac{(\quad)}{12}+\frac{(\quad)}{12}=\frac{(\quad)}{(\quad)}$
$\frac{9}{10}-\frac{1}{6}=\frac{(\quad)}{30}-\frac{(\quad)}{30}=\frac{(\quad)}{(\quad)}$
$\frac{3}{4}+\frac{5}{3}=\frac{(\quad)}{12}+\frac{(\quad)}{12}=\frac{(\quad)}{(\quad)}$
$\frac{9}{10}-\frac{1}{6}=\frac{(\quad)}{30}-\frac{(\quad)}{30}=\frac{(\quad)}{(\quad)}$
答案
2. 9 20 $\frac{29}{12}$ 27 5 $\frac{11}{15}$
解析
$\frac{3}{4} + \frac{5}{3} = \frac{9}{12} + \frac{20}{12} = \frac{29}{12}$
$\frac{9}{10} - \frac{1}{6} = \frac{27}{30} - \frac{5}{30} = \frac{11}{15}$
$\frac{9}{10} - \frac{1}{6} = \frac{27}{30} - \frac{5}{30} = \frac{11}{15}$
3. 计算下面各题。
$ \frac{1}{9} + \frac{1}{6} 1 - \frac{13}{20} \frac{3}{5} + \frac{3}{8} \frac{5}{12} + \frac{1}{3} $
$ \frac{1}{9} + \frac{1}{6} 1 - \frac{13}{20} \frac{3}{5} + \frac{3}{8} \frac{5}{12} + \frac{1}{3} $
答案
3. $\frac{1}{9}$ + $\frac{1}{6}$ 1 - $\frac{13}{20}$
=$\frac{2}{18}$ + $\frac{3}{18}$ =$\frac{20}{20}$ - $\frac{13}{20}$
=$\frac{5}{18}$ =$\frac{7}{20}$
$\frac{3}{5}$ + $\frac{3}{8}$ $\frac{5}{12}$ + $\frac{1}{3}$
=$\frac{24}{40}$ + $\frac{15}{40}$ =$\frac{5}{12}$ + $\frac{4}{12}$
=$\frac{39}{40}$ =$\frac{9}{12}$
=$\frac{3}{4}$
=$\frac{2}{18}$ + $\frac{3}{18}$ =$\frac{20}{20}$ - $\frac{13}{20}$
=$\frac{5}{18}$ =$\frac{7}{20}$
$\frac{3}{5}$ + $\frac{3}{8}$ $\frac{5}{12}$ + $\frac{1}{3}$
=$\frac{24}{40}$ + $\frac{15}{40}$ =$\frac{5}{12}$ + $\frac{4}{12}$
=$\frac{39}{40}$ =$\frac{9}{12}$
=$\frac{3}{4}$
4. 小诊所。(找出错误的原因,并改正)
(1) $\frac{1}{2}+\frac{1}{3}=\frac{1+1}{2+3}=\frac{2}{5}$
(1) $\frac{1}{2}+\frac{1}{3}=\frac{1+1}{2+3}=\frac{2}{5}$
答案
4. (1)把分子、分母直接相加
改正: $\frac{1}{2}$ + $\frac{1}{3}$ = $\frac{3}{6}$ + $\frac{2}{6}$ = $\frac{5}{6}$
(2)结果没有化成最简分数
改正: $\frac{7}{12}$ - $\frac{1}{4}$ = $\frac{7}{12}$ - $\frac{3}{12}$ = $\frac{1}{3}$
改正: $\frac{1}{2}$ + $\frac{1}{3}$ = $\frac{3}{6}$ + $\frac{2}{6}$ = $\frac{5}{6}$
(2)结果没有化成最简分数
改正: $\frac{7}{12}$ - $\frac{1}{4}$ = $\frac{7}{12}$ - $\frac{3}{12}$ = $\frac{1}{3}$
5. (社会生活)王叔叔家5月份的支出中,还房贷占$$ \frac{2}{9} $$,食品支出占$$ \frac{1}{6} $$。这两项支出占总支出的几分之几?
答案
5. $\frac{2}{9}$ + $\frac{1}{6}$ = $\frac{7}{18}$
解析
$\frac{2}{9} + \frac{1}{6} = \frac{4}{18} + \frac{3}{18} = \frac{7}{18}$
6. 一根铁丝,第一次用去$$ \frac{5}{6} $$米,第二次用去$$ \frac{8}{9} $$米,两次一共用去多少米? 第二次比第一次多用多少米?
答案
6. $\frac{5}{6}$ + $\frac{8}{9}$ = $\frac{31}{18}$(米) $\frac{8}{9}$ - $\frac{5}{6}$ = $\frac{1}{18}$(米)
解析
$\frac{5}{6} + \frac{8}{9} = \frac{15}{18} + \frac{16}{18} = \frac{31}{18}$(米)
$\frac{8}{9} - \frac{5}{6} = \frac{16}{18} - \frac{15}{18} = \frac{1}{18}$(米)
$\frac{8}{9} - \frac{5}{6} = \frac{16}{18} - \frac{15}{18} = \frac{1}{18}$(米)
7. 小帆从家走到图书馆,先用7分钟走了全程的$$ \frac{1}{5} $$,又用$$ \frac{3}{10} $$小时走了全程的一半。他已经走了多少小时? 已经走了全程的几分之几?
答案
7. 时间: 7÷60 = $\frac{7}{60}$(时) $\frac{7}{60}$ + $\frac{3}{10}$ = $\frac{5}{12}$(时)
全程的几分之几: $\frac{1}{5}$ + $\frac{1}{2}$ = $\frac{7}{10}$
全程的几分之几: $\frac{1}{5}$ + $\frac{1}{2}$ = $\frac{7}{10}$
8. 在括号里填合适的数,使等式成立。
$ \frac{(\ \ \ \ \ \ )}{(\ \ \ \ \ \ )} + \frac{(\ \ \ \ \ \ )}{(\ \ \ \ \ \ )} = \frac{3}{4} \frac{(\ \ \ \ \ \ )}{(\ \ \ \ \ \ )} + \frac{(\ \ \ \ \ \ )}{(\ \ \ \ \ \ )} = \frac{3}{4} $
$ \frac{(\ \ \ \ \ \ )}{(\ \ \ \ \ \ )} + \frac{(\ \ \ \ \ \ )}{(\ \ \ \ \ \ )} = \frac{3}{4} \frac{(\ \ \ \ \ \ )}{(\ \ \ \ \ \ )} + \frac{(\ \ \ \ \ \ )}{(\ \ \ \ \ \ )} = \frac{3}{4} $
答案
8. 答案不唯一,如 $\frac{1}{2}$ + $\frac{1}{4}$ = $\frac{3}{4}$ $\frac{3}{8}$ + $\frac{3}{8}$ = $\frac{3}{4}$
