AMC12 2002 A

AMC12 2002 A · Q2

AMC12 2002 A · Q2. It mainly tests Linear equations, Word problems (algebra).

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?

老师要求 Cindy 从某个数中减去 3，然后将结果除以 9。但她先减去了 9，然后将结果除以 3，得到答案 43。如果她正确完成问题，答案应该是多少？

(A) 15 15

(B) 34 34

(D) 51 51

(E) 138 138

Answer

Correct choice: (A)

正确答案：（A）

Solution

We work backwards; the number that Cindy started with is $3(43)+9=138$. Now, the correct result is $\frac{138-3}{9}=\frac{135}{9}=15$. Our answer is $\boxed{\textbf{(A) }15}$.

倒推计算；Cindy 开始的数是 $3(43)+9=138$。正确结果是 $\frac{138-3}{9}=\frac{135}{9}=15$。答案是 $\boxed{\textbf{(A) }15}$。

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