gwd 9 2

Kath1985 · 发表于 2011-6-9 19:37:12

9-Q2:

Guy’s net income equals his gross income minus his deductions.By what percent did Guy’s net income change on January 1, 1989, when both his gross income and his deductions increased?

(1)Guy’s gross income increased by 4 percent on January 1, 1989.

(2)Guy’s deductions increased by 15 percent on January 1, 1989.
是E
請問這題要如何列式? 題目要求的是不同時間的收入比嗎?

藜芦 · 发表于 2011-6-10 19:38:10

是的题目要求的是变化前后的净收入的比值
设gross income为x，deductions为y，则初始net income=x-y
条件1 只有gross income的变化无deductions的变化不充分
条件2 只有deductions的变化无gross income的变化不充分
条件1+2 可得变化后的net income=1.04x-1.15y
则net income变化的百分比为[(1.04x-1.15y)-(x-y)]/(x-y)，求不出具体的数值，不充分。
综上，选E

Kath1985 · 发表于 2011-6-13 15:54:34

如果要求出具體數值的話必須提供x 、 y的確切值對吧?

gwd 9 2

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