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![[Post New]](/templates/default/images/icon_minipost_new.gif) 18 Mar 2007 12:29:17 IST
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the number of terms common between the series 1+2+4+8+---------to 100 terms and 1+4+7+10+13+-------to 100 terms is: (A)6 (b)4 (C)5 (d) 8
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18 Mar 2007 17:23:17 IST
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this question has already been solved on the forum... jst check out!!!
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Manasi....
NIT-Allahabad...
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18 Mar 2007 18:43:18 IST
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for a GP;Tn=2^(n-1)
for AP ;Tm=1+(m-1)3.
they are common if
2^(n-1)=3m-2 or [2^(n-2)]+1=[(3m)/2] therefore nas,2^n-1=3m-2;
thus,(n=1,m+1);(n=3,m=2);(n=5,m=6);(n=7,m=22);(n=9,m=86).
and for n=2,4,6,8; m belongs to fraction;which is not possible.
hence 5 is the right answer.
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vision for iit never ends........ |
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