例1 $ 49.6×8.1+2.2×1.05+50.7×1.9 $
答案：49.6×8.1+2.2×1.05+50.7×1.9
= (50 - 0.4)×8.1 + 2.2×1.05 + (50 + 0.7)×1.9
= 50×8.1 - 0.4×8.1 + 2.2×1.05 + 50×1.9 + 0.7×1.9
= 50×(8.1 + 1.9) - 3.24 + 2.31 + 1.33
= 50×10 + (-3.24 + 2.31 + 1.33)
= 500 + 0.4
= 500.4
$ 49.6×8.1+2.2×1.05+50.7×1.9 $
=
49.6×8.1+1.1×2×1.05+(49.6+1.1)×1.9=49.6×8.1+1.1×2.1+49.6×1.9+1.1×1.9=49.6×(8.1+1.9)+1.1×(2.1+1.9)= 496+4.4=500.4
答案：49.6×8.1+1.1×2×1.05+(49.6+1.1)×1.9=49.6×8.1+1.1×2.1+49.6×1.9+1.1×1.9=49.6×(8.1+1.9)+1.1×(2.1+1.9)= 496+4.4=500.4
例2 $ 3.79×0.38+1.59×6.21+3.79×1.21 $
答案：解析：本题考查小数的四则混合运算的简便计算，可利用乘法分配律进行简便运算。
答案：
$3.79×0.38 + 1.59×6.21 + 3.79×1.21$
$= 3.79×(0.38 + 1.21) + 1.59×6.21$
$= 3.79×1.59 + 1.59×6.21$
$= 1.59×(3.79 + 6.21)$
$= 1.59×10$
$= 15.9$
$ 3.79×0.38+3.79×1.21= 3.79×(
0.38
+
1.21
)= 3.79×(
1.59
) $
此时,再运用一次(
乘法分配律
)来进行简便计算。
答案：0.38；1.21；1.59；乘法分配律
$ 3.79×0.38+1.59×6.21+3.79×1.21 $
=
3.79×(0.38+1.21)+1.59×6.21=3.79×1.59+1.59×6.21=1.59×(3.79+6.21)= 1.59×10=15.9
答案：3.79×(0.38+1.21)+1.59×6.21=3.79×1.59+1.59×6.21=1.59×(3.79+6.21)= 1.59×10=15.9
