Question

find the sum of series 101+99+79+.....+47

Answer 1

hey mate!!

here , a= 101 and l=47

so, first we have to find n
d=99-101=-2
an= a+(n-1)d
47=101+(n-1)-2
47-101=-2n+2
-54-2=-2n
-56=-2n
-56/-2=n
n=28

now, sn=n/2(a+l)
sn= 28/2(101+47)
=14(148)
=2072

thus sum is 2072

hope it helps!!

Answer 2

d=99-101
d=-2
an=a+(n-1)d
47=101+(n-1)-2
47=101-2n+2
47=103-2n
47-103=-2n
-56=-2n
28=n ( because minus se minus cancel)
Sn=n/2 (a+l )
=28/2 (101+47)
=14 (148)
=2072


Hope it will help you