1954 AMC 12 第 33 题
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所有题目均经美国数学协会（MAA）官方合法授权使用。
33.
一家银行对一笔 的贷款收取 费用。借款人实际收到 ，并分 个月、每月偿还 。利率约为：
A bank charges for a loan of The borrower receives and repays the loan in installments of a month. The interest rate is approximately:
小提示：
的费用是按每月减少 的未偿余额收取的利息
The charge is interest on a balance that decreases by each month
大提示：
用 与 的平均数近似未偿本金的平均值
Approximate the average outstanding principal by the average of and
解答：
未偿余额从 到 ，每次等额减少 ，所以平均未偿余额约为 因此年费用率约为 最接近的选项是 。
因此，正确答案是 D。
The balance decreases in equal steps from to so its average outstanding value is approximately The annual charge is therefore about The nearest choice is
Thus, the correct answer is D.