AMC8 2002

AMC8 2002 · Q18

AMC8 2002 · Q18. It mainly tests Averages (mean), Arithmetic misc.

Gage skated 1 hr 15 min each day for 5 days and 1 hr 30 min each day for 3 days. How long would he have to skate the ninth day in order to average 85 minutes of skating each day for the entire time?

Gage连续5天每天滑冰1小时15分钟，又连续3天每天滑冰1小时30分钟。为了整个9天平均每天滑冰85分钟，第九天他需要滑冰多长时间？

(A) 1 hr 1小时

(B) 1 hr 10 min 1小时10分

(D) 1 hr 40 min 1小时40分

(E) 2 hr 2小时

Answer

Correct choice: (E)

正确答案：（E）

Solution

In 5 days, Gage skated for 5 × 75 = 375 minutes, and in 3 days he skated for 3×90 = 270 minutes. So, in 8 days he skated for 375+270 = 645 minutes. To average 85 minutes per day for 9 days he must skate 9×85 = 765 minutes, so he must skate 765 −645 = 120 minutes = 2 hours the ninth day.

5天滑冰总时间5 × 75 = 375分钟，3天滑冰3×90 = 270分钟。8天总共滑冰375+270 = 645分钟。要9天平均85分钟/天，总需滑冰9×85 = 765分钟，所以第九天需滑冰765 −645 = 120分钟=2小时。

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