AMC 8 2022 Problem 7

AMC8 2022 年第 7 题

表达式与运算★☆☆☆☆

When the World Wide Web first became popular in the 1990 s, download speeds reached a maximum of about 56 kilobits per second. Approximately how many minutes would the download of a 4.2 -megabyte song have taken at that speed? (Note that there are 8000 kilobits in a megabyte.)

当全球互联网刚开始在 20 世纪 90 年代流行时，下载速度最高为每秒 56 千比特。以这样的速度下载一首 4.2 兆字节的歌曲大约需要多少分钟？（请注意，一兆字节相当于 8000 千比特）

A.0.6
B.10
C.1800
D.7200
E.36000

正确答案 · Correct Answer

解析 · Solution

Solution 1

Notice that the number of kilobits in this song is

4.2 \cdot 8000 = 8 \cdot 7 \cdot 6 \cdot 100.

We must divide this by 56 in order to find out how many seconds this song would take to download:

\displaystyle \frac{\cancel{8}\cdot\cancel{7}\cdot6\cdot100}{\cancel{56}} = 600.

Finally, we divide this number by 60 because this is the number of seconds to get the answer

\displaystyle \frac{600}{60} = 10

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