1 + 6 + 11 + 16 + \ldots + x = 148 – InterviewSolution

1.	1 + 6 + 11 + 16 + \ldots + x = 148
Answer» a=1d=6-1=5n=?Sn=148Sn=n/2[2a+(n-1)d]Sn=n/2[21+(n-1)5]148*2=2n+5n^2-5n5n^2-3n-296=0n=3+-√9+5920/10n=3+-77/10n=3+77/10=80/10=8other value neglected as n cannot be negative

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