百分法(三)

1. 當該數係y

y(1+30%)(1-40%)=117
y*130%*60%=117
y=117/60%/130%
y=150
該數=150

2. 75(1+x%)(1-20%)=81
75(1+x%)*80%=81
1+x%=81/80%/75
1+x%=1.35
x%=0.35
x=35

1.設該數是x
x(1+30%)(1-40%)=117
0.78x=117
x=117/0.78
x=150 所以, 該數是150.
2.75(1+x%)(1-20%)=81
0.8(1+x%)=1.08
1+x%=1.08/0.8
1+x%=1.35
x%=0.35
x=0.35*100
x=35所以,先增加35%.


2008-01-06 18:28:47 補充：
百分法增減:增加=(1+增加%)減少=(1-減少%)

設某數為Y

Y x (1+30/100) x (1 - 40/100) = 117
Y x (130/100) x ( 60/100) = 117 ......(可以約簡就約簡)
Y x (13/10) x (3/5) = 117
Y x (13/10) x (3/5) /(3/5) = 117 / (3/5)
Y x (13/10) /(13/10) =195 / (13/10)
Y = 150


75 x 1+X% x 1-20% = 81
75 x 1+X% x 80% = 81
75 x 1+X% x 80%/80% = 81/80%
75 x 1+X% / 75 = 101.25 /75
1+X% = 1.35
X = 35

1. Let x = 該數
x (1+30%)(1-40%)=117
x(1.3)(0.6)=117
x=150

2. 75 (1+x%)(1-20%)=81
75 (1+x%)(0.8)=81
1+x%=1.35
x%=0.35
x/100=0.35
x=35