AMC8 2006

AMC8 2006 · Q3

AMC8 2006 · Q3. It mainly tests Fractions, Rates (speed).

Elisa swims laps in the pool. When she first started, she completed 10 laps in 25 minutes. Now she can finish 12 laps in 24 minutes. By how many minutes has she improved her lap time?

Elisa 在泳池中游泳。她刚开始时，25 分钟完成 10 圈。现在她 24 分钟完成 12 圈。她提高了多少分钟的单圈时间？

(A) \frac{1}{2} \frac{1}{2}

(B) \frac{3}{4} \frac{3}{4}

(D) 2 2

(E) 3 3

Answer

Correct choice: (A)

正确答案：（A）

Solution

(A) When Elisa started, she completed a lap in $\frac{25}{10}=2.5$ minutes. Now she can complete a lap in $\frac{24}{12}=2$ minutes. She has improved her lap time by $2.5-2=0.5$ or $\frac{1}{2}$ minute.

（A）当 Elisa 刚开始时，她跑完一圈用时 $\frac{25}{10}=2.5$ 分钟。现在她跑完一圈用时 $\frac{24}{12}=2$ 分钟。她的单圈用时提高了 $2.5-2=0.5$ 分钟，即 $\frac{1}{2}$ 分钟。

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