Question

Evaluate the series.

A)125
B) 38
C) 210
D) 165

Answer 1

165 is answer we also use a formula
5 ( n/2(2a + ( n-1)d)
in that n=6 ,a=3 , d= 1

Answer 2

Option D). 165

Explanation:

The given expression is
`\sum_(n=3)^(8)5n`

By using the expression we get an arithmetic series

15, 20, 25........6 terms

Now we will calculate the sum of 6 terms of this sequence

`\sum_(n=3)^(8)5n=6/2[2* 15+(6-1)* 5]`

`=3(30+25)=3* 55=165`

Therefore sum of this sequence is 165.