Question

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? A. 3, 10, 17 B. 3, 23, 43 C. 3 , 36.333 , 70 D. 3, 69.5, 136 2 E. 3, 139, 1,251

Answer 1

Sn = n/2(a + l); where sn is the sum of n terms, n is the number of terms, a is the first term and l is the last term.

1390 = n/2(3 + 136)
2780 = 139n
n = 2780/139 = 20

2nd term = 3 + 20 = 23
3rd term = 23 + 20 = 43

First three terms = 3, 23, 43

option b.