题目内容
递等式计算,写出必要的计算过程,能简便计算的用简便方法计算:
(1)999+2+99+9+9 999+2
(2)6.9×4+310÷25
(3)(3.5+6.5-6.5+3.5)÷4×2.5
(4)(8.6×3.4+3.4×3.4)×2.5
(5)4.8+(1.6÷4+1.2)÷5
(6)6.25÷[(17.2-9×1.8)÷0.016].
(1)999+2+99+9+9 999+2
(2)6.9×4+310÷25
(3)(3.5+6.5-6.5+3.5)÷4×2.5
(4)(8.6×3.4+3.4×3.4)×2.5
(5)4.8+(1.6÷4+1.2)÷5
(6)6.25÷[(17.2-9×1.8)÷0.016].
分析:(1)运用加法交换律与结合律变为999+99+9+9999+(2+2),然后通过数字变形,变为(1000-1)+(100-1)+(10-1)+(10000-1)+4,计算即可;
(2)先算乘除,再算加法;
(3)先算括号内的,然后从左往右依次运算;
(4)括号内运用乘法分配律简算,原式变成12×3.4×2.5,把12看作4×3,运用乘法交换律与结合律简算;
(5)先算括号内的除法,再算括号内的加法,然后算括号外的除法,最后算括号外的加法;
(6)先算小括号内的惩罚,再算小括号内的减法,然后算中括号内的除法,最后算括号外的除法.
(2)先算乘除,再算加法;
(3)先算括号内的,然后从左往右依次运算;
(4)括号内运用乘法分配律简算,原式变成12×3.4×2.5,把12看作4×3,运用乘法交换律与结合律简算;
(5)先算括号内的除法,再算括号内的加法,然后算括号外的除法,最后算括号外的加法;
(6)先算小括号内的惩罚,再算小括号内的减法,然后算中括号内的除法,最后算括号外的除法.
解答:解:1)999+2+99+9+9999+2,
=999+99+9+9999+(2+2),
=(1000-1)+(100-1)+(10-1)+(10000-1)+4,
=11110-3+4,
=11109;
(2)6.9×4+310÷25,
=27.6+12.4,
=40;
(3)(3.5+6.5-6.5+3.5)÷4×2.5,
=(10-6.5+3.5)÷4×2.5,
=7÷4×2.5,
=1.75×2.5,
=4.375;
(4)(8.6×3.4+3.4×3.4)×2.5,
=(8.6+3.4)×3.4×2.5,
=12×3.4×2.5,
=4×3×3.4×2.5,
=(4×2.5)×(3×3.4),
=10×10.2,
=102;
(5)4.8+(1.6÷4+1.2)÷5,
=4.8+(0.4+1.2)÷5,
=4.8+1.6÷5,
=4.8+0.32,
=5.12;
(6)6.25÷[(17.2-9×1.8)÷0.016],
=6.25÷[(17.2-16.2)÷0.016],
=6.25÷[1÷0.016],
=6.25÷62.5,
=0.1.
=999+99+9+9999+(2+2),
=(1000-1)+(100-1)+(10-1)+(10000-1)+4,
=11110-3+4,
=11109;
(2)6.9×4+310÷25,
=27.6+12.4,
=40;
(3)(3.5+6.5-6.5+3.5)÷4×2.5,
=(10-6.5+3.5)÷4×2.5,
=7÷4×2.5,
=1.75×2.5,
=4.375;
(4)(8.6×3.4+3.4×3.4)×2.5,
=(8.6+3.4)×3.4×2.5,
=12×3.4×2.5,
=4×3×3.4×2.5,
=(4×2.5)×(3×3.4),
=10×10.2,
=102;
(5)4.8+(1.6÷4+1.2)÷5,
=4.8+(0.4+1.2)÷5,
=4.8+1.6÷5,
=4.8+0.32,
=5.12;
(6)6.25÷[(17.2-9×1.8)÷0.016],
=6.25÷[(17.2-16.2)÷0.016],
=6.25÷[1÷0.016],
=6.25÷62.5,
=0.1.
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律简便计算.
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