题目内容

计算(能简便要简便)
7.8×10.1 2.8×4.5+6.5×2.8  86.8+9.1÷(2.3-1.6)
9.12×0.25-0.88÷4 1.25×56 34.7÷0.125÷80.
分析:(1)把10.1看作10+0.1,运用乘法分配律简算;
(2)运用乘法分配律简算;
(3)先算括号内的,再算括号外的除法,最后算加法;
(4)先算乘除,再算减法;
(5)把56看作8×7,运用乘法结合律简算;
(6)运用除法的性质简算.
解答:解:(1)7.8×10.1,
=7.8×(10+0.1),
=78+0.78,
=78.78;

(2)2.8×4.5+6.5×2.8,
=2.8×(4.5+6.5),
=2.8×11,
=2.8×(10+1),
=28+2.8,
=30.8;

(3)86.8+9.1÷(2.3-1.6),
=86.8+9.1÷0.7,
=86.8+13,
=99.8;

(4)9.12×0.25-0.88÷4,
=2.28-0.22,
=2.08;

(5)1.25×56,
=1.25×8×7,
=10×7,
=70;

(6)34.7÷0.125÷80,
=34.7÷(0.125×80),
=34.7÷10,
=3.47.
点评:此题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律简便计算.
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