RRB RPF RPSF SI and CONS Model Papers 7 with solutions

Question : 40 of 120

Marks: +1, -0

Which one of the following is a factor of the sum of first twenty-five natural numbers ?

Solution:

(3) Tricky Approach

∵ 1+2+3+...+n= {n(n+1)}/{2}

∵ 1+2+3+. .+25

= {25(25+1)}/{2}=25× 13

Hence, 13 is a factor of required sum.

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