AMC 8 2026 Problem 4
AMC8 2026 年第 4 题
百分比★☆☆☆☆
Brynn's savings decreased by 20% in July, then increased by 50% in August. Brynn's savings are now what percent of the original amount?
Brynn 的存款在七月减少了 20%，然后在八月增加了 50%。现在她的存款是原始金额的百分之多少？
- A.80
- B.90
- C.100
- D.110
- E.120
正确答案 · Correct Answer
E
解析 · Solution
解法1
将两次变化直接相乘：减少 20% 即乘以 0.8，增加 50% 即乘以 1.5。合并：0.8 × 1.5 = 1.2，即原来的 120%，增加了 20%。
假设 Brynn 初始有 100 美元。七月减少 20%，剩 80 美元。八月增加 50%（以 80 为基准），即增加 40 美元，得 120 美元。相比初始 100 美元，增加了 20%。
设初始储蓄为 。七月后：。八月后：。净增 ，即 20%。
Solution 1
Multiply the two changes directly: a 20% decrease means multiply by 0.8, then a 50% increase means multiply by 1.5. Combined: 0.8 × 1.5 = 1.2. This represents a 20% increase from the original amount.
Assume Brynn starts with $100. July: loses 20%, leaving $80. August: gains 50% of $80, which is $40, giving $120. Compared to the original $100, this is a 20% increase.
Let the original savings be . After July: . After August: . The increase is , which is 20%.
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