NIMCET 2009 Question Paper with solutions

Question : 49 of 120

Marks: +1, -0

A teacher gave a student the task of adding '

N^{\prime}

natural numbers starting from 1. After a while, the student reported his result as 700 . The teacher replied that his result was wrong. The student realized that he has added one number twice by mistake. Find the sum of the digits of the number which the student had added twice.

Validate

Solution:

1+2+. . .+N=\;{N(N+1)}/{2}

\;{N(N+1)}/{2}

just less than 700 is abtained for

N=36

and equals 666 .
Thus. number

700-666=34

was added twice.
Hence, sum of digits

=3+4=7

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