Question

12．脫式計(jì)算，怎樣簡(jiǎn)便就怎樣算．
（$\frac{22}{7}$+$\frac{11}{13}$）÷$\frac{11}{13}$                  
7.8×6.9+1.2×6.9+6.9
4.5×12.5%+1.5×$\frac{1}{8}$+1.25                      
$\frac{17}{24}$÷5+$\frac{1}{5}$÷$\frac{24}{7}$+0.2．

Answer 1

分析 ①把除法變成乘法，再用乘法分配律計(jì)算即可；
②用乘法分配律計(jì)算即可；
③把1.25變成0.125×10，再用乘法分配律計(jì)算即可；，
④把除法變成乘法，再用乘法分配律計(jì)算即可；

解答 解：①（$\frac{22}{7}$+$\frac{11}{13}$）÷$\frac{11}{13}$
=（$\frac{22}{7}$+$\frac{11}{13}$）×$\frac{13}{11}$
=$\frac{22}{7}×\frac{13}{11}+\frac{11}{13}×\frac{13}{11}$
=$\frac{26}{7}+1$
=$4\frac{5}{7}$

②7.8×6.9+1.2×6.9+6.9
=（7.8+1.2+1）×6.9
=10×6.9
=69

③4.5×12.5%+1.5×$\frac{1}{8}$+1.25
=4.5×0.125+1.5×0.125+0.125×10
=（4.5+1.5+10）×0.125
=16×0.125
=2×（8×0.125）
=2×1
=2

④$\frac{17}{24}$÷5+$\frac{1}{5}$÷$\frac{24}{7}$+0.2
=$\frac{17}{24}×\frac{1}{5}+\frac{1}{5}×\frac{7}{24}+\frac{1}{5}$
=$\frac{1}{5}×（\frac{17}{24}+\frac{7}{24}+1）$
=$\frac{1}{5}×2$
=$\frac{2}{5}$

點(diǎn)評(píng) 脫式計(jì)算要先觀察算式的特點(diǎn)，靈活運(yùn)用運(yùn)算定律簡(jiǎn)便計(jì)算．