Question

Find s7 for 3 8 13 18

Answer 1

I know u are supposed to use formulas to do this...but it is just as easy to do it this way...that is, if u dont have many numbers...if u were looking for s20, we would have used formulas...lol
u will notice that in ur pattern, their is a difference of 5 between each number....this is an arithmetic sequence

start at 3
3 + 5 = 8
8 + 5 = 13
13 + 5 = 18
18 + 5 = 23
23 + 5 = 28
28 + 5 = 33
thats ur first 7 numbers...so just add them and u will have s7
s7 = 126

Answer 2

126

Explanation:

Given sequence is 3,8,13, 18..........

We need to find the sum of 7 terms s7

Sum formula is
`S_n=(n)/(2) (2a+(n-1)d)`

Where 'a' is the first term and 'd' is the difference

Difference of two terms is 8-3=5, 13-8= 5

d=5 and a=3

To find s7 , the value of n=7

`S_7=(7)/(2) (2(3)+(7-1)5)=126`

The sum of 7 terms = 126