题目内容

脱式计算,能简算要简算.
2.74+2.74+…+2.74
共40个
)×0.25

4.5×100.2
3.2×1.25×2.5 6.9×3.84+3.84×3.1
4.8+5.2×0.85 0.8×(3.2-2.99÷2.3)
分析:(1)括号内改写成2.74×40,然后运用乘法结合律简算;
(2)把100.2看作(100+0.2),运用乘法分配律简算;
(3)把3.2看作4×0.8,运用乘法交换律与结合律简算;
(4)运用乘法分配律简算;
(5)先算乘法,再算加法;
(6)先算括号内的除法,再算括号内的减法,最后算乘法.
解答:解:(1)(
2.74+2.74+…+2.74
共40个
)×0.25,
=2.74×40×0.25,
=2.74×(40×0.25),
=2.74×10,
=27.4;

(2)4.5×100.2,
=4.5×(100+0.2),
=4.5×100+0.9,
=450+0.9,
=450.9;

(3)3.2×1.25×2.5,
=4×0.8×1.25×2.5,
=(0.8×1.25)×(4×2.5),
=1×10,
=10;

(4)6.9×3.84+3.84×3.1,
=3.84×(3.1+6.9),
=3.84×10,
=38.4;

(5)4.8+5.2×0.85,
=4.8+4.42,
=9.22;

(6)0.8×(3.2-2.99÷2.3),
=0.8×(3.2-1.3),
=0.8×1.9,
=1.52.
点评:考查了小数的四则混合运算,注意运算顺序和运算法则,灵活运用所学的运算定律简便计算.
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