③.
【分析】①根据减去两个数的和等于连续减去这两个数来简算;
②先把分数和百分数都会化成小数,再运用乘法分配律简算;
③=×(1),=×(﹣),=×()…由此化简求解.
【解答】解:①9﹣(3+0.4),
=9﹣3﹣,
=9﹣﹣3,
=9﹣3,
=5;
②1.8×+2.2×25%,
=1.8×0.25+2.2×0.25,
=(1.8+2.2)×0.25,
=4×0.25,
=1;
③,
=×(1﹣)+×(﹣)+…+×(﹣)+×(﹣),
=×(1﹣+﹣+…+﹣+﹣),
=×(1﹣),
=×,
=.
【点评】第三题这类型的题目关键是找到规律,再根据规律化简求解.
23.脱式计算
①6.25﹣40÷16×2.5
②+(4﹣3)÷
③(8﹣10.5×)÷4
④2÷[5﹣4.5×(20%+)].
【分析】算式①可根据乘法交换律计算式中的“40÷16×2.5”.
算式②③根据四则混合运算的运算顺序计算即可:先算乘除,再算加减,有括号的要先算括号里面的;
算式④可根据乘法分配律计算算式中的“4.5×(20%+)”.
【解答】解:①6.25﹣40÷16×2.5
=6.25﹣40×2.5÷16,
=6.25﹣100÷16,
=6.25﹣6.25,
=0;
②+(4﹣3)÷
=+(﹣)×,
=+×,
=+2,
=2;
③(8﹣10.5×)÷4