AMC10 2013 B
AMC10 2013 B · Q4
AMC10 2013 B · Q4. It mainly tests Arithmetic sequences basics.
When counting from 3 to 201, 53 is the 51st number counted. When counting backwards from 201 to 3, 53 is the nth number counted. What is n ?
从3数到201时，53是第51个数。从201倒数到3时，53是第n个数。n是多少？
(A)
146
146
(B)
147
147
(C)
148
148
(D)
149
149
(E)
150
150
Answer
Correct choice: (D)
正确答案：（D）
Solution
Answer (D): The number 201 is the 1st number counted when proceeding backwards from 201 to 3. In turn, 200 is the 2nd number, 199 is the 3rd number, and $x$ is the $(202-x)^{\text{th}}$ number. Therefore 53 is the $(202-53)^{\text{th}}$ number, which is the $149^{\text{th}}$ number.
答案（D）：从 201 倒数到 3 时，201 是数到的第 1 个数。依次，200 是第 2 个数，199 是第 3 个数，而 $x$ 是第 $(202-x)^{\text{th}}$ 个数。因此，53 是第 $(202-53)^{\text{th}}$ 个数，也就是第 $149^{\text{th}}$ 个数。
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