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Best answer
9 votes
9 votes
This series can be written as
(1 + 2 + 3 + ......to 50 terms) - (6 + 7 + 8 + .....to 50 terms)
Both these are in AP’s

a =1, n =50, d= 1  for first series
a= 6, n =50 , d= 1 for second series

using AP formula  n/2[ 2a + (n-1)d ] the 100th term is  -250
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16 votes
16 votes
Just group each 2 numbers from left hand side. Summation of each 2 numbers will give -5 here.

(1-6)+(2-5)+(3-8)+....upto 50 terms.(as we grouped 2 numbers each time)

=-5-5-5-...50 terms

=-5*50= -250
Answer:

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