题目内容

3.计算.
235+275-126          (5.9+1.65)÷2.5         5.95÷(1.2+0.5)×5
325÷25×20            25×80×0.04           ($\frac{1}{5}$+$\frac{1}{2}$)÷($\frac{1}{4}$-$\frac{1}{5}$)
$\frac{1}{6}$×5.16+5.16×$\frac{5}{6}$

分析 (1)235+275-126先算加法再算减法,
(2)(5.9+1.65)÷2.5先算加法再算除法,
(3)5.95÷(1.2+0.5)×5再算加法再算除法,最后算乘法,
(4)325÷25×20先算除法再算乘法,
(5)25×80×0.04先算25×0.04的1,再算1×80,
(6)($\frac{1}{5}$+$\frac{1}{2}$)÷($\frac{1}{4}$-$\frac{1}{5}$)先算两个小括号里面的,再算除法,
(7)$\frac{1}{6}$×5.16+5.16×$\frac{5}{6}$先算$\frac{1}{6}+\frac{5}{6}$=1,再算1×5.16.

解答 解:(1)235+275-126 
=510-126
=384

(2)(5.9+1.65)÷2.5  
=7.55÷2.5
=3.02

(3)5.95÷(1.2+0.5)×5
=5.95÷1.7×5
=3.5×5
=17.5

(4)325÷25×20
=13×20
=260

(5)25×80×0.04
=25×0.04×80
=1×80
=80

(6)($\frac{1}{5}$+$\frac{1}{2}$)÷($\frac{1}{4}$-$\frac{1}{5}$)  
=$\frac{7}{10}÷\frac{1}{20}$
=$\frac{7}{10}×20$
=14

(7)$\frac{1}{6}$×5.16+5.16×$\frac{5}{6}$
=5.16×($\frac{1}{6}+\frac{5}{6}$)
=5.16

点评 考查学生的运用简便方法进行计算的能力,要灵活选用简便方法,所以掌握运算定律的特征是解答的基础.

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