题目内容

用递等式计算.(能简算的要写出简算过程)
(1)1.25×3.2×0.25 (2)6.4×0.27+3.6×0.27
(3)3.84-0.84×5÷1.5 (4)2.5×0.99
(5)8.19+0.5×(4.36-2.74) (6)1.8×2.48+1.52×1.8-0.5
(7)[(6-4.2)×2.5]÷2.5×1 (8)4.02÷[(1-0.4)÷0.1].
分析:(1)先把3.2分解成8×0.4,再运用乘法结合律简算;
(2)(6)运用乘法分配律简算;
(3)先算乘法,再算除法,最后算减法;
(4)先把0.99分解成(1-0.01),再运用乘法分配律简算;
(5)先算小括号里面的减法,再算乘法,最后算加法;
(7)先算小括号里面的减法,再运用乘法结合律简算;
(8)先算小括号里面的减法,再算中括号里面的除法,最后算括号外的除法.
解答:解:(1)1.25×3.2×0.25,
=1.25×8×0.4×0.25,
=(1.25×8)×(0.4×0.25),
=10×0.1,
=1;

(2)6.4×0.27+3.6×0.27,
=(6.4+3.6)×0.27,
=10×0.27,
=2.7;

(3)3.84-0.84×5÷1.5,
=3.84-4.2÷1.5,
=3.84-2.8,
=1.04;

(4)2.5×0.99,
=2.5×(1-0.01),
=2.5×1-2.5×0.01,
=2.5-0.025,
=2.475;

(5)8.19+0.5×(4.36-2.74),
=8.19+0.5×1.62,
=8.19+0.81,
=9;

(6)1.8×2.48+1.52×1.8-0.5,
=1.8×(2.48+1.52)-0.5,
=1.8×4-0.5,
=7.2-0.5,
=6.8;

(7)[(6-4.2)×2.5]÷2.5×1,
=[1.8×2.5]÷2.5×1,
=1.8×(2.5÷2.5)×1,
=1.8×1×1,
=1.8;

(8)4.02÷[(1-0.4)÷0.1],
=4.02÷[0.6÷0.1],
=4.02÷6,
=0.67.
点评:本题考查了四则混合运算,注意运算顺序和运算法则,灵活运用所学的运算定律进行简便计算.
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