脱式计算(能简算的要用简便方法计算):① 80÷(1-84%)② 5-5×+③ 0.25×32×12.5%④ ÷+×.
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解:①80÷(1-84%),
=80÷0.16,
=500;
②5-5×+,
=5-2+,
=3;
③0.25×32×12.5%,
=0.25×4×8×0.125,
=(0.25×4)×(8×0.125),
=1×1,
=1;
④÷+×,
=×+×,
=(+)×,
=1×,
=.
解析分析:①硝酸括号内的,再算括号外的;
②先算乘法,再算减法和加法;
③把32看作4×8,运用乘法结合律简算;
④把除法改为乘法,运用乘法分配律简算.
点评:此题考查了运算定律与简便运算,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.