选一个做吧【用简便方法做】1.15.37乘7.88减9.37乘7.88减15.37乘2.12加9.37乘2.122.80.35乘0.25加4.197乘2.5加0.2903乘25加0.0865乘25

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选一个做吧【用简便方法做】1.15.37乘7.88减9.37乘7.88减15.37乘2.12加9.37乘2.122.80.35乘0.25加4.197乘2.5加0.2903乘25加0.0865乘25

选一个做吧【用简便方法做】1.15.37乘7.88减9.37乘7.88减15.37乘2.12加9.37乘2.122.80.35乘0.25加4.197乘2.5加0.2903乘25加0.0865乘25
选一个做吧【用简便方法做】
1.15.37乘7.88减9.37乘7.88减15.37乘2.12加9.37乘2.12
2.80.35乘0.25加4.197乘2.5加0.2903乘25加0.0865乘25

选一个做吧【用简便方法做】1.15.37乘7.88减9.37乘7.88减15.37乘2.12加9.37乘2.122.80.35乘0.25加4.197乘2.5加0.2903乘25加0.0865乘25
1. 15.37 * 7.88 - 9.37 * 7.88 - 15.37 * 2.12 + 9.37 * 2.12
=(15.37 - 9.37)* 7.88 -(15.37- 9.37)* 2.12 (提公因式)
=(15.37 - 9.37)* (7.88 - 2.12) (提公因式)
=6* 5.76=34.56
2. 80.35 * 0.25 + 4.197 * 2.5 + 0.2903 * 25 + 0.0865 * 25
(观察两个小数个位是5,两个分别是3、7,凑10)
= 0.8035 * 25 + 0.0865 * 25 + 0.4197 * 25 + 0.2903 * 25
=(0.8035 + 0.0865) * 25 +(0.4197 + 0.2903) * 25(提公因式)
=0.89*25+0.71*25
=(0.89+0.71)*25(提公因式)
=1.6*25=40