用简便算法算

8.42*9.6+0.4*842
=8.42×9.6+0.4×100×8.42
=8.42×(9.6+0.4×100)
=8.42×(9.6+40)
=8.42×49.6

是不是题有错？如果题是：
8.42×9.6+0.4×8.42
=8.42×9.6+0.4×8.42
=8.42×(9.6+0.4)
=8.42×10
=84.2

8.42*9.6+0.4*842
=84.2*(0.96+4)
=84.2*(5-0.04)
=84.2*5-84.2*(0.05-0.01)
=421-4.21+0.842
=416.79+0.842
=417.632

8.42*9.6+0.4*842
= 8.42*9.6+40*8.42
=(9.6+40)*8.42
= 49.6*8.42
= 417.632

842*(9.6+0.4)

8.42*100*9.6/100+0.4*842
=842*(0.096+0.4)
=842*0.496
=842*(0.496+0.004-0.004)
=842*(0.5-0.004)
=421-3.368
=417.632

吧提取公因式8.42，把842写成8.42*100，