Maths 百分法

7.设1月为x,即4月为x(1+12%)(1-5%)(1-5%)

百分变化=[x(1+12%)(1-5%)(1-5%)-x]/x
=(1+12%)(1-5%)(1-5%)-1
=+1.08%

8.设某數为y
y(1-40%)(1+x%)=81___(1)
y(1-x%)(1+40%)=63___(2)

联立方程

y=81/[(1-40%)(1+x%)]__(3)put in to (2)

81(1-x%)(1+40%)/[(1-40%)(1+x%)]=63
81(1-x%)(1+40%)=63(1-40%)(1+x%)
113.4-1.134x=37.8+0.378x
1.512x=75.6
x=50

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