SOLUTION: Determine the number of terms in the arithmetic series where a1=19, an=89 and Sn= 810

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Question 896969: Determine the number of terms in the arithmetic series where a1=19, an=89 and Sn= 810
Answer by richwmiller(17219) About Me  (Show Source):
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a1=19, an=89 and Sn= 810
S = ½(a1 + an)n
810 = ½(19 + 89)n
810 = ½(108)n
810 = 54n
n=15
89 = 19 + (14)d
70=14d
d=5
19,24,29,34,39,
44,49,54,59,64,
69,74,79,84,89