Question

9.8乘以25、0.038乘以5乘以2.1（简便计算）

急 在星期一之前给我答案

Answer 1

1、9.8*25
=(10-0.2)*25
=250-5
=245
2、0.038*5/2.1
=0.019*2*5/2.1
=0.19/2.1
=19/210

Answer 2

9.8*25=(10-0.2)*25=250-5=245
0.038*5*2.1=0.038*5*(2+0.1)=0.038*(10+0.5)=0.38+0.038*0.5=0.38+(1-0.002)*0.5=0.38+0.5-0.001=0.879
方法就是通过整数的变形来算，*号就是乘号的意思

Answer 3

9.8*25=10*25-0.2*25=250-5=245
0.038*5*2.1=(0.04*5-0.002*5)*(2+0.1)=(0.2-0.01)(2+0.1)=(2+0.1)(2-0.1)/10=(4-0.01)/10=3.99/10=0.399

Answer 4

9.8*25=(1-0.2)*25=250-5=245