AMC10 2004 B
AMC10 2004 B · Q7
AMC10 2004 B · Q7. It mainly tests Linear equations, Fractions.
On a trip from the United States to Canada, Isabella took $d$ U.S. dollars. At the border she exchanged them all, receiving 10 Canadian dollars for every 7 U.S. dollars. After spending 60 Canadian dollars, she had $d$ Canadian dollars left. What is the sum of the digits of $d$?
伊莎贝拉从美国去加拿大旅行时带了 $d$ 美元。在边境她把它们全部兑换，每 7 美元换得 10 加元。花费 60 加元后，她还剩 $d$ 加元。$d$ 的各位数字之和是多少？
(A)
5
5
(B)
6
6
(C)
7
7
(D)
8
8
(E)
9
9
Answer
Correct choice: (A)
正确答案：（A）
Solution
Isabella received $\frac{10d}{7}$ Canadian dollars at the border and spent 60 of them. Thus $\frac{10d}{7} - 60 = d$, from which it follows that $d = 140$, and the sum of the digits of $d$ is 5.
伊莎贝拉在边境换得 $\frac{10d}{7}$ 加元，并花费了其中的 60 加元。因此 $\frac{10d}{7} - 60 = d$，由此得出 $d = 140$，$d$ 的各位数字之和是 5。
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