SOLUTION: I have tried to do the problem "For each arithmetic series, find S of 25" 3+7+11+15 This is the equation i came up with 25[2(3)+(25-1)d/2] I just cant find the d and when i

Question 36866This question is from textbook Algebra 2
: I have tried to do the problem
"For each arithmetic series, find S of 25"
3+7+11+15
This is the equation i came up with
25[2(3)+(25-1)d/2]
I just cant find the d and when i try my answer comes out incorrect..
thanks.. This question is from textbook Algebra 2

Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
For each arithmetic series, find S of 25"
3+7+11+15
S(25) means to find the sum of the 1st 25 terms.
d is the difference between any term and the previous term:
For your problem d=11-7=4
The Sum formula is S(n)=(n/2)(a(1)+a(n))
and a(n)=a(1)+(n-1)d
Since a(1)=3, a(25)=3+(24)(4)=99
Therefore S(25)=(25/2)(3+99)=25(51)=1275
Cheers,
stan H.
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