第76頁練一練1. 3.2×1.5+4.8÷2.5 0.42÷[(3.2-0.5)÷9] =4.8+1.92 =0.42÷[2.7÷9] =6.72 =0.42÷0.3 =1.4【解析】作業(yè)精靈老師提示：①在沒有括號(hào)的算式里，先算乘除再算加減。②在有括號(hào)的算式里，先算括號(hào)里的，最先算小括號(hào)其次算中括號(hào)。2. 0.73×0.25×4 0.37+1.79+0.63 7.6×0.8＋7.6×0.2 =0.73×（0.25×4） =（0.37+0.63）＋1.79 =7.6×（0.8+0.2） =0.73×1 =1+1.79 =7.6×1 =0.73 =2.79 =7.6練習(xí)十四1. 3.5 12 0.02 0.006 0.42 1.92. 2.55÷1.7－0.59 （1.2+1.3）÷0.25 =1.5－0.59 =2.5÷0.25 =0.91 =10 3.4÷(0.5+0.3×4) 6.48÷[(1.4-0.8)×0.9] =3.4÷(0.5+1.2) =6.48÷[0.6×0.9] =3.4÷1.7 =6.48÷0.54 =2 =123. 5.78+0.84+0.16 12.5×0.96×8 =5.78+(0.84+0.16) =12.5×8×0.96 =5.78+1 =100×0.96 =6.78 =96 1.27+3.9+0.73+6.1 0.25×36 =（1.27+0.73）+（3.9+6.1） =0.25×4×9 =2+10 =1×9 =12 =9 1.28×8.6-0.28×8.6 2.4×1.02 =（1.28－0.28）×8.6 =2.4×（1+0.02） =1×8.6 =2.4×1+2.4×0.02 =8.6 =2.4+0.048 =2.4484. 17.4+18.8+18.6+17.2=72（秒） 答：她們的總成績?yōu)?2秒。5. 400×0.25×0.35=35（千克） 答：可以榨油35千克。6. 9-4.37-0.63 0.45÷0.6÷0.5 =4.63-0.63 =0.75÷0.5 =4 =1.5 9-（4.37+0.63） 0.45÷（0.6×0.5） =9-5 =0.45÷0.3 =4 =1.57. 5.52－0.55－0.45 5.5×4.8＋5.2×5.5 =5.52－（0.55+0.45） =5.5×（4.8+5.2） =5.52－1 =5.5×10 =4.52 =55 8.1÷（0.9×0.3） 2.12－（1.12＋3×0.33） =8.1÷0.9÷0.3 =2.12-（1.12+0.99） =9÷0.3 =2.12－1.12-0.99 =30