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1. 想一想,填一填。
(1) $5×8= 40$
(
(2) $\frac{3}{4}×3= \frac{9}{4}$
(
(1) $5×8= 40$
(
40
)÷(5
)= (8
) (40
)÷(8
)= (5
) (2) $\frac{3}{4}×3= \frac{9}{4}$
(
$\frac{9}{4}$
)÷($\frac{3}{4}$
)= (3
) ($\frac{9}{4}$
)÷(3
)= ($\frac{3}{4}$
)答案
40
5
8
40
8
5
$\frac{9}{4}$
$\frac{3}{4}$
3
$\frac{9}{4}$
3
$\frac{3}{4}$
5
8
40
8
5
$\frac{9}{4}$
$\frac{3}{4}$
3
$\frac{9}{4}$
3
$\frac{3}{4}$
2. 判断。(对的打“√”,错的打“×”。)
(1) $\frac{1}{3}÷2= \frac{1}{3}×2= \frac{2}{3}$ (
(2) $\frac{5}{8}÷4= \frac{5}{8÷4}= \frac{5}{2}$ (
(3) $\frac{8}{9}÷4= \frac{8÷4}{9}= \frac{2}{9}$ (
(4) 如果$b$是不等于0的自然数,那么$\frac{1}{7}÷b= \frac{1}{7}×\frac{1}{b}$。 (
(1) $\frac{1}{3}÷2= \frac{1}{3}×2= \frac{2}{3}$ (
×
) (2) $\frac{5}{8}÷4= \frac{5}{8÷4}= \frac{5}{2}$ (
×
) (3) $\frac{8}{9}÷4= \frac{8÷4}{9}= \frac{2}{9}$ (
√
) (4) 如果$b$是不等于0的自然数,那么$\frac{1}{7}÷b= \frac{1}{7}×\frac{1}{b}$。 (
√
)答案
×
×
√
√
×
√
√
3. 下列各题有没有错误？如果有,错在哪里？请你改正过来。
$\frac{2}{5}÷4= \frac{4÷2}{5}= \frac{2}{5}$
$\frac{5}{9}÷5= \frac{5}{9}÷\frac{1}{5}= \frac{5}{45}$
$\frac{1}{12}÷6= \frac{1}{12}×6= \frac{1}{2}$
$\frac{4}{5}÷3= \frac{4}{5}×\frac{1}{3}= \frac{4}{15}$
$\frac{2}{5}÷4= \frac{4÷2}{5}= \frac{2}{5}$
$\frac{5}{9}÷5= \frac{5}{9}÷\frac{1}{5}= \frac{5}{45}$
$\frac{1}{12}÷6= \frac{1}{12}×6= \frac{1}{2}$
$\frac{4}{5}÷3= \frac{4}{5}×\frac{1}{3}= \frac{4}{15}$
答案
×
$ \frac 25÷4=\frac 25×\frac 14=\frac 1{10}$
×
$ \frac 59÷5=\frac {5÷5}9=\frac 19$
×
$ \frac 1{12}÷6=\frac 1{12}×\frac 16=\frac 1{72}$
√
$ \frac 25÷4=\frac 25×\frac 14=\frac 1{10}$
×
$ \frac 59÷5=\frac {5÷5}9=\frac 19$
×
$ \frac 1{12}÷6=\frac 1{12}×\frac 16=\frac 1{72}$
√
