Find d page no.

This question comes in this year nac test
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A person was given a task to calculate sum of all the page no's of a novel , but by mistake he added one page no twice ,therefore at the end he got sum 1000 ,now you have to find that page no which was added twice by him.
 

Hiral.s

Par 100 posts (V.I.P)
sum of 'n' page numbers starting from one is given by n(n+1)/2.
so n(n+1)/2<1000
n(n+1)<2000.
for n=44 we get the maximum value below 2000 ( which is 1980)
so the sum will be 44*45/2=990.
so 10 has been added twice
 
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