AMC8 1994

AMC8 1994 · Q17

AMC8 1994 · Q17. It mainly tests Rates (speed), Arithmetic sequences basics.

Pauline Bunyan can shovel snow at the rate of 20 cubic yards for the first hour, 19 cubic yards for the second, 18 for the third, etc., always shoveling one cubic yard less per hour than the previous hour. If her driveway is 4 yards wide, 10 yards long, and covered with snow 3 yards deep, then the number of hours it will take her to shovel it clean is closest to

Pauline Bunyan 第一小时铲雪20立方码，第二小时19立方码，第三小时18立方码，依此类推，每小时比前一小时少铲1立方码。如果她的车道宽4码，长10码，雪深3码，她铲干净需要的时间最接近

(A) 4 4

(B) 5 5

(D) 7 7

(E) 12 12

Answer

Correct choice: (D)

正确答案：（D）

Solution

Volume 4×10×3=120 cu yd. Sum first 7 hours: 20+19+...+14=119, closest to 120.

体积4×10×3=120立方码。前7小时总和：20+19+...+14=119，最接近120。

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