A sequence of numbers is written in the following fashion: 1, 7, 1, 1, 7, 7, 1, 1, 1, 7, 7, 7, ... till ‘n’ terms. The sum of first 5001 terms of the given sequence is

Question

Answer 1

Hi Peeyush,
If we take 1 and 7 as a set
Number of terms = 2+4+6......... ~5001
n(n+1) ~5001
70(71) = 4970
hence, in the end there will be 70 1's and 70 7's and 31 1's after that
Sum = 31(1)+(4970/2)(8) =19911
Hope that helps.
Thanks,
Varun.

Answer 2

Hi Peeyush,
If we take 1 and 7 as a set
Number of terms = 2+4+6......... ~5001
n(n+1) ~5001
70(71) = 4970
hence, in the end there will be 70 1's and 70 7's and 31 1's after that
Sum = 31(1)+(4970/2)(8) =19911
Hope that helps.
Thanks,
Varun.

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A sequence of numbers is written in the following fashion: 1, 7, 1, 1, 7, 7, 1, 1, 1, 7, 7, 7, ... till ‘n’ terms. The sum of first 5001 terms of the given sequence is