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How many terms are in the arithmetic sum 15 + 18 + 21 + … + 99? n = 1,653 n = 28 n = 27 n = 29
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5 votes
How many terms are in the arithmetic sum 15 + 18 + 21 + … + 99?

n = 1,653


n = 28


n = 27


n = 29

User Louay Sleman
by
8.3k points

1 Answer

4 votes
The n-th term is
a(n) = 15 + 3(n-1)
Then the last term corresponds to the value n that satisfies
99 = 15 +3(n -1)
33 = 5 +(n -1)
29 = n

The appropriate choice is ...
n = 29
User Mdnfiras
by
9.4k points
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