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Official Quant Thread for CAT 2012 Quantitative

Please continue here for all the Quant queries and discussions.
The links to the previous threads are:
Part 1
http://www.pagalguy.com/forum/quantitative-questions-and-answers/74662-official-quant-thread-cat-2012-a.html
Part 2
http://www.pagalguy.com/forum/quantitative-questions-and...
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@mani0303 said: Try this: the sum of the series - 1,5,14,28,47... until 10th term
sn = 1+5+14+28+47 + ....+tn

sn = 1+5 +14+28+ ... +tn-1 +tn [Shift it by 1]

Subtract..

0 = 1+(4+9+14+19+... (n-1) terms) - tn [See in brackets the terms are in AP]

=> tn =1 + (n-1)/2*(2*4 +(n-2)*5)

Now multiply and get tn in form of n.

Just do sigma over 1 to 10.

p.s: __/\__ @[470280:gs4890] bhai , @[367896:sumeet1489] bhai aur sabhi quant maharathi ...
Pain is inevitable,Suffering is optional.  
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Page 3494 of 3736