Question

Solve...................
(85+90+95+............. +715)

Answer 1

heya..!!!

given that:-

a = 85
d = 90 - 85 = 5

l = 715

715 = 85 + (n - 1)×5

=> 715 - 85 = (n - 1)×5

=> 630/5 = (n - 1)

=> n = 126 + 1


=> n = 127

sn = n/2[a + l]

=> 127/2(85 + 715)

=> 127/2(800)

=> Sn = 127× 400

=> Sn = 50800

Answer 2

a = 85
d = 5
an = 715
an = a + ( n- 1 ) d
715 = 85 + 5n - 5
5n = 715 - 80
n = 635 / 5
n = 127
So,
Sn = n / 2 ( a + l)
= 127 /2 ( 85 + 715 )
So Sn = 127× 400
Sn = 50800
_____ hope it helps