# arithmetic

posted by Cennie

In an arithmetic series, the terms of the series are equally spread out. For example, in
1 + 5 + 9 + 13 + 17, consecutive terms are 4 apart. If the first term in an arithmetic series is
3, the last term is 136, and the sum is 1,390, what are the first 3 terms?

1. Reiny

have you learned this property ?

S(n) = (n/2)(first + last) ?
1390 = (n/2)(3 + 136)
I get n = 20

so term(20) = a+19d = 136
19d = 133
d = 7

term 1 = 3
term 2 = 10
term 3 = 17

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