2. 一台榨油机$\frac {3}{4}小时榨油\frac {2}{5}$吨,照这样计算,$\frac {8}{3}$小时可以榨油多少吨？下面列式正确的是(
A.$\frac {3}{4}÷\frac {2}{5}×\frac {8}{3}$
B.$\frac {3}{4}÷\frac {8}{3}×\frac {2}{5}$
C.$\frac {2}{5}÷\frac {3}{4}×\frac {8}{3}$
D.$\frac {8}{3}÷\frac {3}{4}÷\frac {2}{5}$
C
)。A.$\frac {3}{4}÷\frac {2}{5}×\frac {8}{3}$
B.$\frac {3}{4}÷\frac {8}{3}×\frac {2}{5}$
C.$\frac {2}{5}÷\frac {3}{4}×\frac {8}{3}$
D.$\frac {8}{3}÷\frac {3}{4}÷\frac {2}{5}$
答案：C 【提示】先求出每小时榨油$(\frac{2}{5}÷ \frac{3}{4})$吨，再乘$\frac{8}{3}$小时即可。
3. 杯中原来有800毫升水,小明将杯中的水倒出一些(如右图),从杯中倒出了多少毫升水？正确的列式是(
A.$800×\frac {3}{5}$
B.$800×\frac {3}{8}$
C.$800÷(1-\frac {3}{8})$
D.$800-800×\frac {3}{8}$
D
)。A.$800×\frac {3}{5}$
B.$800×\frac {3}{8}$
C.$800÷(1-\frac {3}{8})$
D.$800-800×\frac {3}{8}$
答案：D 【提示】原来水的高度占 8 格，现在水的高度占 3 格，占原来水的$\frac{3}{8}$，所以从杯中倒出了$(800-800× \frac{3}{8})$毫升水。
4. 30千克先增加$\frac {1}{5}$,再减少$\frac {1}{5}$,结果是(
A.30
B.32
C.28
D.28.8
D
)千克。A.30
B.32
C.28
D.28.8
答案：D 【提示】先增加$\frac{1}{5}$是在 30 千克的基础上增加$\frac{1}{5}$，即增加$\frac{1}{5}$后是$30× (1+\frac{1}{5})$千克；又减少$\frac{1}{5}$是在$30× (1+\frac{1}{5})$千克的基础上减少$\frac{1}{5}$，即减少$\frac{1}{5}$后是$30× (1+\frac{1}{5})× (1-\frac{1}{5})=28.8$(千克)。
5. 某车间有男职工24人,若女职工比男职工多$\frac {1}{8}$,则全车间有职工多少人？正确的算式是(
A.$24+24×\frac {1}{8}$
B.$24×(1+1+\frac {1}{8})$
C.$24÷\frac {1}{8}-24$
D.$24×(1-\frac {1}{8})$
B
)。A.$24+24×\frac {1}{8}$
B.$24×(1+1+\frac {1}{8})$
C.$24÷\frac {1}{8}-24$
D.$24×(1-\frac {1}{8})$
答案：B 【提示】根据题意，把男职工的人数看作单位“1”，则女职工的人数是男职工的$(1+\frac{1}{8})$，所以全车间职工的人数是男职工的$(1+1+\frac{1}{8})$。然后用男职工的人数乘全车间职工的人数占男职工的人数的分率，即可求解。
6. 扩建一个长方形操场,长和宽都增加$\frac {1}{3}$,扩建后的操场面积是原来的(
A.$\frac {1}{3}$
B.$\frac {3}{2}$
C.$\frac {16}{9}$
D.$\frac {4}{3}$
C
)。A.$\frac {1}{3}$
B.$\frac {3}{2}$
C.$\frac {16}{9}$
D.$\frac {4}{3}$
答案：C 【提示】扩建后的操场面积是原来的$(1+\frac{1}{3})× (1+\frac{1}{3})=\frac{16}{9}$。
7. 加工同一种零件,甲$\frac {4}{5}$小时加工80个,乙加工20个要用15分钟,两人的加工速度相比较,(
A.甲快
B.乙快
C.一样快
D.无法确定
A
)。A.甲快
B.乙快
C.一样快
D.无法确定
答案：A 【提示】根据“工作效率=工作总量÷工作时间”，分别计算出甲、乙两人的工作效率，再比较即可。
1. 计算下面各题,能简算的要简算。
$\frac {12}{7}-(\frac {1}{3}÷\frac {7}{15}+\frac {4}{5})$
$\frac {9}{5}×\frac {3}{7}-\frac {4}{5}÷\frac {7}{3}$
$(\frac {2}{23}+\frac {2}{71})×23+\frac {25}{71}$
$47×\frac {13}{46}$
$(\frac {1}{2}+\frac {1}{6}-\frac {1}{9})÷\frac {1}{18}$
$(\frac {1}{11}+\frac {1}{13})×13×11$
$\frac {12}{7}-(\frac {1}{3}÷\frac {7}{15}+\frac {4}{5})$
$\frac {9}{5}×\frac {3}{7}-\frac {4}{5}÷\frac {7}{3}$
$(\frac {2}{23}+\frac {2}{71})×23+\frac {25}{71}$
$47×\frac {13}{46}$
$(\frac {1}{2}+\frac {1}{6}-\frac {1}{9})÷\frac {1}{18}$
$(\frac {1}{11}+\frac {1}{13})×13×11$
答案：$\frac{1}{5}$ $\frac{3}{7}$ 3 $13\frac{13}{46}$ 10 24
解析：
$\frac{12}{7}-(\frac{1}{3}÷\frac{7}{15}+\frac{4}{5})$
$=\frac{12}{7}-(\frac{1}{3}×\frac{15}{7}+\frac{4}{5})$
$=\frac{12}{7}-(\frac{5}{7}+\frac{4}{5})$
$=\frac{12}{7}-\frac{5}{7}-\frac{4}{5}$
$=1-\frac{4}{5}$
$=\frac{1}{5}$
$\frac{9}{5}×\frac{3}{7}-\frac{4}{5}÷\frac{7}{3}$
$=\frac{9}{5}×\frac{3}{7}-\frac{4}{5}×\frac{3}{7}$
$=(\frac{9}{5}-\frac{4}{5})×\frac{3}{7}$
$=1×\frac{3}{7}$
$=\frac{3}{7}$
$(\frac{2}{23}+\frac{2}{71})×23+\frac{25}{71}$
$=\frac{2}{23}×23+\frac{2}{71}×23+\frac{25}{71}$
$=2+\frac{46}{71}+\frac{25}{71}$
$=2+1$
$=3$
$47×\frac{13}{46}$
$=(46+1)×\frac{13}{46}$
$=46×\frac{13}{46}+1×\frac{13}{46}$
$=13+\frac{13}{46}$
$=13\frac{13}{46}$
$(\frac{1}{2}+\frac{1}{6}-\frac{1}{9})÷\frac{1}{18}$
$=(\frac{1}{2}+\frac{1}{6}-\frac{1}{9})×18$
$=\frac{1}{2}×18+\frac{1}{6}×18-\frac{1}{9}×18$
$=9+3-2$
$=10$
$(\frac{1}{11}+\frac{1}{13})×13×11$
$=\frac{1}{11}×13×11+\frac{1}{13}×13×11$
$=13+11$
$=24$
$=\frac{12}{7}-(\frac{1}{3}×\frac{15}{7}+\frac{4}{5})$
$=\frac{12}{7}-(\frac{5}{7}+\frac{4}{5})$
$=\frac{12}{7}-\frac{5}{7}-\frac{4}{5}$
$=1-\frac{4}{5}$
$=\frac{1}{5}$
$\frac{9}{5}×\frac{3}{7}-\frac{4}{5}÷\frac{7}{3}$
$=\frac{9}{5}×\frac{3}{7}-\frac{4}{5}×\frac{3}{7}$
$=(\frac{9}{5}-\frac{4}{5})×\frac{3}{7}$
$=1×\frac{3}{7}$
$=\frac{3}{7}$
$(\frac{2}{23}+\frac{2}{71})×23+\frac{25}{71}$
$=\frac{2}{23}×23+\frac{2}{71}×23+\frac{25}{71}$
$=2+\frac{46}{71}+\frac{25}{71}$
$=2+1$
$=3$
$47×\frac{13}{46}$
$=(46+1)×\frac{13}{46}$
$=46×\frac{13}{46}+1×\frac{13}{46}$
$=13+\frac{13}{46}$
$=13\frac{13}{46}$
$(\frac{1}{2}+\frac{1}{6}-\frac{1}{9})÷\frac{1}{18}$
$=(\frac{1}{2}+\frac{1}{6}-\frac{1}{9})×18$
$=\frac{1}{2}×18+\frac{1}{6}×18-\frac{1}{9}×18$
$=9+3-2$
$=10$
$(\frac{1}{11}+\frac{1}{13})×13×11$
$=\frac{1}{11}×13×11+\frac{1}{13}×13×11$
$=13+11$
$=24$