Question

第12题和第14题怎么做?

Answer 1

12题=1.997*1000+1.997*100+1.997*10+1.997*1 = 1.997*1111 = 1111*2-1111*0.003 = 2222 - 3.333 = 2218.667
14题等差数列=(1.1+9.9) * 9 / 2 = 11 * 9 / 2 = 49.5
或者=1.1+ 9.9 + 2.2 + 8.8 + 3.3 + 7.7 + 4.4 + 6.6 + 5.5
=(5.5-4.4)+(5.5+4.4)+...+(5.5-1.1)+(5.5+1.1)+5.5
=5.5*9=49.5

Answer 2

12。1997+199.7+19.97+1.997
=2000-3+200-0.3+20-0.03-2-0.003
=（2000+200+20+2）-（3+0.3+0.03+0.003）
=2222-3.333
=2218.667。
14。1.1+2.2+3.3+4.4+5.5+6.6+7.7+8.8+9.9
=1.1x(1+2+3+4+5+6+7+8+9)
=1.1x(4x10+5)
=1.1x45
=49.5。