脱式计算. 6.5×8+3.5×8-44 | 8.5+(5.6-4.8)×13 | 1.9-1.9×(1.9-1.9) |
![]() ![]() | 1×![]() ![]() ![]() | ![]() ![]() |
49.5×![]() ![]() | ![]() ![]() ![]() ![]() ![]() | ![]() ![]() ![]() |
897×![]() | [![]() ![]() ![]() ![]() | ![]() ![]() ![]() ![]() ![]() |
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解:
(1)6.5×8+3.5×8-44,
=(6.5+3.5)×8-44,
=10×8-44,
=80-44,
=36;
(2)8.5+(5.6-4.8)×13,
=8.5+0.8×13, =8.5+10.4, =18.9; (3)1.9-1.9×(1.9-1.9), =1.9-1.9×0, =1.9-0, =1.9; (4) ![]() ![]() =( ![]() ![]() =2×29, =58; (5)1× ![]() ![]() ![]() = ![]() ![]() =20× ![]() =2; (6) ![]() ![]() =(101-1)× ![]() =100× ![]() =28; (7)49.5× ![]() ![]() =49.5×10.6-49.5×0.6, =49.5×(10.6-0.6), =49.5×10, =495; (8) ![]() ![]() ![]() ![]() ![]() = ![]() ![]() ![]() ![]() ![]() =( ![]() ![]() ![]() =11× ![]() =7; (9) ![]() ![]() ![]() = ![]() ![]() ![]() = ![]() ![]() = ![]() ![]() = ![]() (10)897× ![]() =897×0.375-0.375+104×0.375, =(897-1+104)×0.375, =1000×0.375, =375; (11)[ ![]() ![]() ![]() ![]() =[ ![]() ![]() ![]() ![]() ![]() =[ ![]() ![]() ![]() ![]() =[ ![]() ![]() ![]() = ![]() ![]() = ![]() (12) ![]() ![]() ![]() ![]() ![]() =(9+99+999+9999)+ ![]() =9+99+999+9999+4, =(9+1)+(99+1)+(999+1)+(9999+1), =10+100+1000+10000, =11110; (13) ![]() ![]() ![]() = ![]() ![]() ![]() =2- ![]() = ![]() |
分析:
(1)先根据四则混合运算的顺序确定应该先算什么后算什么:只有一级运算时,从左到右计算;有两级运算时,先算乘除,后算加减.有一层括号时,先算括号里的;有多层括号时,先算小括号里的. (2)能够运用简便算法的题目,根据所学定律选择适合的简便方法. |
点评:此题主要考察四则混合运算的顺序和简便算法的灵活运用,要根据每一题的特点选择适合的方法.
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