能簡便的要簡便計(jì)算
2.9×1.4+2×0.16 200-(3.05+7.1)×18 2.5×32×1.25
(2.44-1.8)÷0.4×20 48×10.1 3.2×19+3.2.
解:(1)2.9×1.4+2×0.16,
=4.06+0.32,
=4.38;
(2)200-(3.05+7.1)×18,
=200-10.15×18,
=200-182.7,
=17.3;
(3)2.5×32×1.25,
=2.5×4×8×1.25,
=(2.5×4)×(8×1.25),
=10×10,
=100;
(4)(2.44-1.8)÷0.4×20,
=0.64÷0.4×20,
=1.6×20,
=32;
(5)48×10.1,
=48×(10+0.1),
=48×10+48×0.1,
=480+4.8,
=484.8;
(6)3.2×19+3.2,
=3.2×(19+1),
=3.2×20,
=64.
分析:(1)先同時(shí)運(yùn)算乘法,再算加法;
(2)先算小括號(hào)里面的加法,再算括號(hào)外的乘法,最后算減法;
(3)先把32分解成4×8然后運(yùn)用乘法結(jié)合律簡算;
(4)先算小括號(hào)的減法,再算括號(hào)外的除法,最后算乘法;
(5)把10.1分解成10+0.1然后用乘法分配律簡算;
(6)運(yùn)用乘法分配律簡算.
點(diǎn)評(píng):運(yùn)算定律是常用的簡便運(yùn)算的方法,要熟練掌握,靈活運(yùn)用.