Question

Find the sum of the 1st 100 terms: 100+98+96+......
50
100
-98
1000

Answer 1

100

Explanation:

Given :

Terms ( n ) = 100

First term ( a ) = 100

Series = > 100 + 98 + 96 .......

Common difference ( d ) = 98 - 100 = > - 2

We know sum formula:

S_n = ( n / 2 ) ( 2 a + ( n - 1 ) d )

= > S_100 = ( 100 / 2 ) ( 200 + ( 100 - 1 ) - 2 )

= > S_100 = 50 ( 200 - 198 )

= > S_100 = 50 ( 2 )

= > S_100 = 100

Therefore, sum of first 100 terms is 100.