215+85÷17-12           125×24           158+64+142+236
400÷(120-20×4)156-78-22[720÷(13+27)]×12

解:(1)215+85÷17-12,
=215+5-12,
=208;

(2)125×24,
=125×8×3,
=1000×3,
=3000;

(3)158+64+142+236,
=(158+142)+(64+236),
=300+300,
=600;

(4)400÷(120-20×4),
=400÷(120-80),
=400÷40,
=10;

(5)156-78-22,
=156-(78+22),
=156-100,
=56;

(6)[720÷(13+27)]×12,
=[720÷40]×12,
=18×12,
=216.
分析:(1)先算除法,再算加法和減法;
(2)把24看作8×3,運(yùn)用乘法結(jié)合律簡算;
(3)運(yùn)用加法交換律與結(jié)合律簡算;
(4)先算括號內(nèi)的乘法,再算括號內(nèi)的減法,最后算括號外的除法;
(5)運(yùn)用減法的性質(zhì)簡算;
(6)先算小括號內(nèi)的,再算中括號內(nèi)的,最后算括號外的.
點(diǎn)評:此題主要考查整數(shù)的四則混合運(yùn)算的運(yùn)算順序,以及應(yīng)用運(yùn)算定律進(jìn)行簡便計(jì)算.
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