1986年第二届AMC8试题答案 - 初中竞赛 我爱数学网-数学爱好者的家园-中国专业化的数学论坛之一

[AMC8] 1986年第二届AMC8试题答案

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 本帖最后由 meidun 于 2014-10-30 21:10 编辑 美国AMC8历年试题 1986年第二届AMC8试题答案 AACCD EBEEB ADCCB AEBDD ECBBD 难题讲解： (10)The center of the picture is 1.5 feet from the edge of the picture, and 9.5 feet from the end of the wall, so our answer is 9.5-1.5=8, or (B). (15)The sale price of the coat is 50% of $180 or$90. The additional discount is 20% of $90 or$18, so the Saturday price is $90-$18=\$72, or answer choice (B). (18)The fewest number of posts is used if the wall serves as the longer side of the rectangular grazing area. Thus there are 6 posts on the 60 meter side (including the corners) and 3 more posts on each 36 meter side for a total of 12 posts, or answer (B). (21)You can do it with A and therefore, with H as well simply by folding everything in a straight line. You can also do it with B by folding the non-lettered sides up, and then the B-side around. Hence you can do it for F as well. You can also do it for D and E by folding everything straight over in a line. However, it can't be done for C and G so 6 (E) of them work. (24)Al must be assigned to one of the lunch groups. The probability that Bob is assigned to the same lunch group is approximately 1/3, and the probability that Carol is assigned to that same group is also approximately 1/3. Thus the probability that all three are assigned to the same group is approximately 1/3*1/3=1/9, or (B). (25)In a set of whole numbers which are equally spaced, the average of the numbers in the set is the average of the smallest number and the largest number. For example, the average of {1,3,5,7,9}=(1+9)/2=5, and the average of {2,5,8,11,14,17}=(2+17)/2=9.5. In this problem, the averages are: A: (2+100)/2=51B: (3+99)/2=51 C: (4+100)/2=52 D: (5+100)/2=52.5 E: (6+96)/2=51 so the answer is (D).

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