解:
98+67=175;
4.8-0.79=4.01;

+0.2=

+

=

+

=

;
15-5

=

-

=9

;
1.25×8=10;
1÷0.25=4;

×1

=

×

=

;
7.2÷4=

×

=

=1

;
2.5×1

×0.4
=1

×(2.5×0.4)
=1

×1
=1

;
1- - =0; ÷ -1= ×2-1= - = ; | | | | 12×( - )=12×( - ) =12× =1. | | | | | | | |
| | |
分析:整數(shù)的加法,減法的計(jì)算方法是一樣的.都是相同數(shù)位上的數(shù)字相加減,在豎式計(jì)算時(shí),把相同數(shù)位對(duì)齊;小數(shù)的計(jì)算方法和整數(shù)的計(jì)算方法是一樣的,小數(shù)計(jì)算時(shí)要注意就小數(shù)點(diǎn)對(duì)齊,然后相同數(shù)位相加減即可. 分?jǐn)?shù)的加法的計(jì)算方法是:同分母的,分母不變,分子相加.異分母的,先化成同分母的,還是分母不變,分子相加.分?jǐn)?shù)的減法就是:同分母的分母不變,分子相減.異分母的化為同分母,然后分子相減.
小數(shù)乘法的計(jì)算:先按整數(shù)乘法的法則算出積;再看因數(shù)中一共有幾位小數(shù),就從得數(shù)的右邊起數(shù)出幾位,點(diǎn)上小數(shù)點(diǎn).在得數(shù)的小數(shù)部分末尾有0,一般要把0去掉.
分?jǐn)?shù)乘法的計(jì)算:把各個(gè)分?jǐn)?shù)的分子乘起來(lái)作為分子,各個(gè)分?jǐn)?shù)的分母相乘起來(lái)作為分母,(即乘上這個(gè)分?jǐn)?shù)的倒數(shù)),然后再約分.
除數(shù)是整數(shù)的小數(shù)除法的計(jì)算:(1)按照整數(shù)除法的法則去除,商的小數(shù)點(diǎn)要和被除數(shù)的小數(shù)點(diǎn)對(duì)齊;(2)如果除到被除數(shù)的末尾仍有余數(shù),就在余數(shù)后面補(bǔ)零,再繼續(xù)除.
除數(shù)是小數(shù)的小數(shù)除法的計(jì)算:(1)先看除數(shù)中有幾位小數(shù),就把被除數(shù)的小數(shù)點(diǎn)向右移動(dòng)幾位,數(shù)位不夠的用零補(bǔ)足;(2)然后按照除數(shù)是整數(shù)的小數(shù)除法來(lái)除
分?jǐn)?shù)的除法的計(jì)算:(1)用被除數(shù)的分子與除數(shù)的分母相乘作為分子;(2)用被除數(shù)的分母與除數(shù)的分子相乘作為分母.
點(diǎn)評(píng):本組試題主要是整數(shù)、小數(shù)、分?jǐn)?shù)的加減乘除運(yùn)算,考察點(diǎn)側(cè)重小數(shù)分?jǐn)?shù)的互化及運(yùn)用定律進(jìn)行簡(jiǎn)便計(jì)算.