4 votes 4 votes The value of the expression $1 - 6 + 2 - 7 + 3 - 8 +$……… to $100$ terms is __________. GATE tbb-mockgate-2 numerical-answers quantitative-aptitude arithmetic-series + – Bikram asked Jan 24, 2017 retagged Sep 12, 2020 by ajaysoni1924 Bikram 468 views answer comment Share Follow See all 0 reply Please log in or register to add a comment.
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 Bikram answered Jan 24, 2017 selected Jan 30, 2017 by Aboveallplayer Bikram comment Share Follow See 1 comment See all 1 1 comment reply Lakshman Bhaiya commented Oct 18, 2019 reply Follow Share Sum of $AP $, if the last term is given, then $S_{n} = \frac{n}{2}(a+l)$ Where $a=$first term, $l=$last term, $n=$total number of terms. 1 votes 1 votes Please log in or register to add a comment.
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 Gaurab Ghosh answered Jan 26, 2017 Gaurab Ghosh comment Share Follow See all 0 reply Please log in or register to add a comment.