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【OG20-P176-197题】
In the first week of the year, Nancy saved $1. In each of the next 51 weeks, she saved $1 more than she had saved in the previous week. What was the total amount that Nancy saved during the 52 weeks?
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该题平均耗时:1m42s ,平均正确率:87.3%。
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当前版本由
ya**** 更新于2015-12-01 22:19:10 感谢由
ya**** 对此题目的解答所做出的贡献。
一共有52个数,第一个数是1,最后一个是52,可把这52个数分成和为53的26组数(52+1=53,51+2=53...),所以和为53*26=1378
题目讨论 (5条评论)

提交
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贾思敏
(1)a1=1,d=1,Sn=1+2+3……+n=n(n+1)/2 (2)a1=1,d=2,奇数项相加,Sn=1+3+5+……+n=n^2
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0 回复 2021-09-24 18:10:28
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贾思敏
等差数列前n项和公式为:Sn=n*a1+n(n-1)d/2 或 Sn=n(a1+an)/2
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0 回复 2021-09-24 18:02:12
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babyweezy
算出来结果是8的
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0 回复 2019-08-29 10:30:09
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嘻嘻嘻521
n(n+1)/2
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0 回复 2018-11-27 14:42:23
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七七姑娘
直接等差数列求和
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0 回复 2018-06-09 16:05:44