/

AMC8 2024

AMC8 2024 · Q8

AMC8 2024 · Q8. It mainly tests Basic counting (rules of product/sum), Counting & probability misc.

On Monday, Taye has $\$2$. Every day, he either gains $\$3$ or doubles the amount of money he had on the previous day. How many different dollar amounts could Taye have on Thursday, $3$ days later?
周一,Taye 有 $\$2$。每天,他要么增加 $\$3$,要么将前一天的钱数翻倍。到周四(3 天后),Taye 可能拥有的不同美元金额有多少种?
(A) 3 3
(B) 4 4
(C) 5 5
(D) 6 6
(E) 7 7
Answer
Correct choice: (D)
正确答案:(D)
Solution
How many dollar values could be on the first day? Only $2$ dollars. The second day, you can either add $3$ dollars, or double, so you can have $5$ dollars, or $4$. For each of these values, you have $2$ values for each. For $5$ dollars, you have $10$ dollars or $8$, and for $4$ dollars, you have $8$ dollars or $7$ dollars. Now, you have $2$ values for each of these. For $10$ dollars, you have $13$ dollars or $20$, for $8$ dollars, you have $16$ dollars or $11$, for $8$ dollars, you have $16$ dollars or $11$, and for $7$ dollars, you have $14$ dollars or $10$. On the final day, there are 11, 11, 16, and 16 repeating, leaving you with $8-2 = \boxed{\textbf{(D) 6}}$ different values.
第一天可能金额只有 $2$ 美元。第二天的可能金额:加 $3$ 得 $5$ 美元,或翻倍得 $4$ 美元。对于每种金额,第三天又有两种选择。对于 $5$ 美元:$10$ 或 $8$;对于 $4$ 美元:$8$ 或 $7$。第四天,对于 $10$:$13$ 或 $20$;对于 $8$:$16$ 或 $11$;对于 $8$:$16$ 或 $11$;对于 $7$:$14$ 或 $10$。 最终,重复的 $11$、$11$、$16$、$16$,共有 $8-2 = \boxed{\textbf{(D) 6}}$ 种不同值。
Topics
Related Questions
Practice full AMC exams on amcdrill.
Try full-length practice and diagnostics at www.amcdrill.com.