Question

Sarah 将四盎司咖啡倒入一个八盎司杯中，又将四盎司奶油倒入另一个同样大小的杯子。她把第一杯中一半的咖啡倒入第二杯，充分搅拌后，再把第二杯中一半的液体倒回第一杯。现在第一杯中的液体有几分之几是奶油？

Sarah pours four ounces of coffee into an eight-ounce cup and four ounces of cream into a second cup of the same size. She then transfers half the coffee from the first cup to the second and, after stirring thoroughly, transfers half the liquid in the second cup back to the first. What fraction of the liquid in the first cup is now cream?

$\dfrac{1}{4}$

$\dfrac{1}{3}$

$\dfrac{3}{8}$

$\dfrac{2}{5}$

$\dfrac{1}{2}$

答案：D

知识点：混合问题过程模拟

难度评级：1450

解答：

第一次转移 $2$ 盎司咖啡后，第 $1$ 杯有 $2$ 盎司咖啡，第 $2$ 杯有 $2$ 盎司咖啡和 $4$ 盎司奶油，共 $6$ 盎司。

从第 $2$ 杯倒回一半，即 $3$ 盎司，其中含 $1$ 盎司咖啡和 $2$ 盎司奶油，留下第 $1$ 杯有 $3$ 盎司咖啡和 $2$ 盎司奶油。奶油所占比例为 $\dfrac{2}{2+3}=\dfrac{2}{5}$ 。

所以正确答案是 D。

After transferring $2$ oz of coffee, cup $1$ has $2$ oz coffee and cup $2$ has $2$ oz coffee plus $4$ oz cream, a total of $6$ oz.

Transferring back half of cup $2$ (that is $3$ oz, consisting of $1$ oz coffee and $2$ oz cream) leaves cup $1$ with $3$ oz coffee and $2$ oz cream. The fraction that is cream is $\dfrac{2}{2+3}=\dfrac{2}{5}.$

Thus, the correct answer is D.

2002 AMC 10A 第 17 题

答案：D

难度评级：1450

解答：

其他年份的第 17 题