遞等式計算:(能用簡便方法計算的要用簡便方法計算)
0.11×1.8+8.2×0.11
0.8×(3.2-2.99÷2.3)
3.5-3.5×0.98
12.5×2.5×3.2
(8.1-5.4)÷3.6+85.7.
解:(1)0.11×1.8+8.2×0.11,
=0.11×(1.8+8.2),
=0.11×10,
=1.1;
(2)0.8×(3.2-2.99÷2.3),
=0.8×(3.2-1.3),
=0.8×1.9,
=1.52;
(3)3.5-3.5×0.98,
=(1-0.98)×3.5,
=0.02×3.5,
=0.07;
(4)12.5×2.5×3.2,
=12.5×2.5×4×0.8,
=12.5×0.8×(2.5×4),
=10×10,
=100;
(5)(8.1-5.4)÷3.6+85.7,
=2.7÷3.6+85.7,
=0.75+85.7,
=86.45.
分析:(1)(3)運用乘法分配律的逆運算簡算;
(2)先算括號內(nèi)的除法,再算括號內(nèi)的減法,最后算括號外的乘法;
(4)把3.2看作4×0.8,運用乘法交換律與結(jié)合律簡算;
(5)先算括號內(nèi)的,再算括號外的除法,最后算加法.
點評:考查了四則混合運算的運算順序和運算法則,靈活運用所學(xué)的運算定律簡便計算.