Question

Find the sum of all odd numbers between 700 and 900.

Answer 1

Hey friend

First odd no. between 700&900= 701 (a1)
Last odd no. between 700&900= 899(al)
Difference=2(d)

By formula
An= a+(n-1)d

=>899=701+(n-1)*2
=>899=701+2n-2
=>899=699+2n
=>200=2n
=>n=100

Now, by formula
Sn=n/2(a+l)

=>Sn=>100/2(701+899)
=>Sn=>100/2*1600
=>Sn=>100*800
=>Sn=>80000

So, the sum of all odd no. between
700 and 900=80000

Answer 2

HEY MATE
HERE IS YOUR ANSWER

701,703,705.........899

Here, a= 701 , d = 703-701 = 2 , tn = 899

tn = a+ ( n-1 ) d
899= 701+ ( n- 1) 2
899= 701 +2n-2
899 = 699 + 2n
899-699=2n.
200/2 = n
n = 100

Sn = n/2 [2a+ (n-1)d]
=100/2 [2×701 + (100-1)2]
=50 [ 1402 + 99× 2]
= 50 [ 1402 + 198 ]
=50 [ 1600 ]
= 80000

Hence the sum of all odd numbers between 700 and 900 is 80000

HOPE IT HELPS