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Intern
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Does PS include questions on sequences and series? Also, [#permalink]
 05 Dec 2003, 09:32
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Does PS include questions on sequences and series?
Also, can someone help me with this one -
Q -What is the sum of reciprocal of first thirty positive integers?
Thx
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Director
Joined: 28 Oct 2003
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What is the sum of reciprocal of first thirty positive integers?
I don't know a shortcut to get the right answer, but if the question is multiple choice: I'd look at the answers, and if they're spaced widely enough, compute the sum of the first ten reciprocals + 10(1/15) +10(1/25).
I'm curious as to whether someone will have a more elegant and fast solution.
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Thanks!
This might sound silly but how did you get 10(1/50) and 10(1/25)?
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Director
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10(1/15) is an approximation of the sum of 1/11+1/12+1/13...+1/20
10(1/25) is an approximation of the sum of 1/21+1/22+1/23...+1/30
I just picked the midpoint.
Converting 1-10 to decimals (3 places) is easy if you have them memorized.
1+.5+.333+.25+.2+.167+.143+.125+.111+.1 =
2.92
+10/15 +10/25
+.667+.400
3.987, approximately...
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Director
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Per Microsoft Excel, the exact solution is
9304682830147/2329089562800
Or, in decimal form, 3.994987130920390
I learned that Excel has an LCM function.
Considering how much of my employer's time I just wasted, I am ashamed of myself.
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close
