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by ajith » Thu Feb 04, 2010 1:49 am
bhumika.k.shah wrote:OG 12th edition Q # 116
In the case of 5 cities we have = 4+3+2+1 = 4*5/2 =10

so, in the case of 30 cities we will have = 29+28....+1 = 29*30/2 =435

B

[sum of all positive integers till n = n(n+1)/2 ]
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by thephoenix » Thu Feb 04, 2010 1:51 am
there will tot 30C2 enteries=435

its like selecting two city out of 30
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by neelimareddym » Thu Feb 04, 2010 2:08 am
IMO B..

1st person -> 29 cities
2nd person -> 28 cities (1 city already covered by 1st person)
3rd person -> 27 cities (2 cities already covered by 1st and 2nd person)
...
... so on

So, Total = (29+28+27+26+....+3+2+1) = (29*30)/2 = 435
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by bhumika.k.shah » Thu Feb 04, 2010 6:00 am
Thanks guys!

Its the concept that is more important for me to know than to know how did one get the answer.

:-)
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