Question

9．計算下面各題，能簡算的要用簡便方法計算．
1.25×7.8×0.8
2.78×99+1.78
101×5.78-5.78．

Answer 1

分析 ①運用乘法交換律可簡便計算，
②先運用乘法分配律計算，再算加法，
③逆用乘法分配律可簡算．

解答 解：①1.25×7.8×0.8
=1.25×0.8×7.8
=1×7.8
=7.8

②2.78×99+1.78
=2.78×（100-1）+1.78
=2.78×100-2.78×1+1.78
=278-2.78+1.78
=275.22+1.78
=277

③101×5.78-5.78
=（101-1）×5.78
=100×5.78
=578

點評 此題考查小數(shù)四則混合運算順序和靈活運用運算定律，分析數(shù)據(jù)找到正確的計算方法．