百分數增減

1.let y be the number
y(1+15%)(1-10%)
=y(1.15)(0.9)
=1.035y
(1.035y-y/y)*100%
=0.035*100%
=3.5%
2.let y be the number
y(1+20%)(1-20%)
=y(1.2)(0.8)
=0.96y
(0.96y-y/y)*100%
=-0.04*100%
=-4%

2007-12-01 18:02:59 補充：
唔明既sd mail問我!

2007-12-02 07:33:48 補充：
第2題有錯...更正2.let y be the numbery(1 20%)(1 20%)=y(1.2)(1.2)=1.44y(1.44y-y/y)*100%=-0.44*100%=4.4%

1.Yx1.15x0.9

2.Yx1.2x1.2

1.100+150-100=150
2.100+200+200=500