Question
Person A wrote first N consecutive natural numbers on a board and found their sum. Another Person B came and deleted the smallest number and found the sum of remaining numbers. The process continued until just N remained on the board. The average of all the sums is found to out to be 105. Find N.
Answer: Option A
:
A
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A
The problem can be expressed as follows:
1+2+3+4+5................n 2+3+4+5................n 3+4+5................n
This is nothing but =∈n2n.
It is given that: n(n+1)(2n+1)6n=(n+1)(2n+1)6=105
Solving we get:
2n2+3n-629=0 or (2n+37)(n-17)=0 or n=17.
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