AMC 8 1997 Problem 18

AMC8 1997 年第 18 题

百分比★★★☆☆

At the grocery store last week, small boxes of facial tissue were priced at 4 boxes for $5 . This week they are on sale at 5 boxes for $4 . The percent decrease in the price per box during the sale was closest to

上周在杂货店，小盒面巾纸的售价为 4 盒 $5。本周它们打折出售，5 盒 $4。打折期间每盒价格下降的百分比最接近

A.30%
B.35%
C.40%
D.45%
E.65%

正确答案 · Correct Answer

解析 · Solution

Solution 1

Last week, each box was

\displaystyle \frac{5}{4} = 1.25

This week, each box is

\displaystyle \frac{4}{5} = 0.80

Percent decrease is given by

\displaystyle \frac{X_{old} - X_{new}}{X_{old}} \cdot 100\%

This, the percent decrease is

\displaystyle \frac{1.25 - 0.8}{1.25} \cdot 100\% = \frac{45}{125} \cdot 100\% = 36\%

, which is closest to

B

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