SOLUTION: 25+28+31+.....+100 to solve the sum

Question 772070: 25+28+31+.....+100 to solve the sum
Answer by John10(297) (Show Source): You can put this solution on YOUR website!
Hi,
This is arithmetic sequence because the common difference:
d = 28 - 25 = 31- 28 =...= 3
Apply the formula
a(n) = a(1) + (n- 1)d
100 = 25 + (n - 1)3
100 = 25 + 3n - 3
3n - 3 = 75
3n = 78
n = 26
So we have 26 terms totally
To find the sum, apply the formula:
S(n) = n(a(1) + a(n))/2
= (26/2)( 25 + 100)
= (13)(125)
= 1625
Hope it helps you!
John10 (john100185@yahoo.com)
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