Question

老师要求 Cindy 从某个数中减去 $3$ ，再将结果除以 $9$ 。可她却先减去 $9$ ，再将结果除以 $3$ 得到答案 $43$ 。如果她按正确步骤计算，答案应是多少？

Cindy was asked by her teacher to subtract $3$ from a certain number and then divide the result by $9.$ Instead, she subtracted $9$ and then divided the result by $3,$ giving an answer of $43.$ What would her answer have been had she worked the problem correctly?

$15$

$34$

$43$

$51$

$138$

答案：A

知识点：逆推法一次方程

难度评级：1020

解答：

设原数为 $x$ 。Cindy 计算了 $\dfrac{x-9}{3} = 43$ ，所以 $x - 9 = 129$ ， $x = 138$ 。

正确计算为 $\dfrac{138-3}{9} = \dfrac{135}{9} = 15$ 。

因此，正确答案是 A。

Let $x$ be the number. Cindy computed $\dfrac{x-9}{3} = 43,$ so $x - 9 = 129$ and $x = 138.$

The correct computation gives $\dfrac{138-3}{9} = \dfrac{135}{9} = 15.$

Thus, the correct answer is A.

2002 AMC 12A 第 2 题

答案：A

难度评级：1020

解答：

其他年份的第 2 题