2001 AMC 12竞赛试题/第03题
Problem
The state income tax where Kristin lives is levied at the rate of 
of the first 
of annual income plus 
of any amount above . Kristin noticed that the state income tax she paid amounted to 
of her annual income. What was her annual income?
Solution
Let the income amount be denoted by 
.
We know that 
.
We can now try to solve for :
So the answer is 
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