計算下面各題,能簡算的要寫出簡算過程.
①6.72+2.08×4×1.5
②12.56÷2.5÷0.4
③2.85×4.7+28.5×0.53
④9.88÷[5×(7.34-6.96)]
⑤2.5×3.2×1.25
⑥0.56×99.
解:①6.72+2.08×4×1.5,
=6.72+2.08×6,
=6.72+12.48,
=19.2;
②12.56÷2.5÷0.4,
=12.56÷(2.5×0.4),
=12.56÷1,
=12.56;
③2.85×4.7+28.5×0.53,
=2.58×4.7+(28.5÷10)×(0.53×10),
=2.58×4.7+2.85×.5.3,
=2.58×(4.7+5.3),
=2.58×10,
=25.8;
④9.88÷[5×(7.34-6.96)],
=9.88÷(5×7.34-5×6.96),
=9.88÷(36.7-34.8),
=9.88÷1.9,
=5.2;
⑤2.5×3.2×1.25,
=(2.5×0.4)×(8×1.25),
=1×10,
=10;
⑥0.56×99,
=0.56×(100-1),
=0.56×100-0.56,
=56-0.56,
=55.44.
分析:①6.72+2.08×4×1.5,按運算順序算,算乘法時可利用乘法結(jié)合律先算4×1.5;
②12.56÷2.5÷0.4,可利用一個數(shù)連除以兩個數(shù)等于這個數(shù)除以這兩個數(shù)的積;
③2.85×4.7+28.5×0.53,先利用積不變規(guī)律,再利用乘法分配律進(jìn)行簡算;
④9.88÷[5×(7.34-6.96)],中括號里利用乘法分配律進(jìn)行簡算;
⑤2.5×3.2×1.25,得用乘法結(jié)合律進(jìn)行簡算;
⑥0.56×99,先把99看成100-1,再利用乘法分配律進(jìn)行簡算.
點評:此題考查了在計算過程中如果有簡便的算法簡算會更快更準(zhǔn)確,所以平時要把基本的方法掌握好.