A sequence is such that \(a_1=1\) and \(a_n=a_{n-1}+n\). Which of the following could be the sum of two consecutive terms of the sequence?

A. 60
B. 64
C. 72
D. 80
E. 99
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I don't understand this question. If we say each term increases by 2 (n=2), we get can get almost any value in the answer choices. For example 31 + 33 = 64 or 39 + 41 = 80

kchen1994

Actually each term is not increasing by 2, it is increasing by the term n, said that

a_1 = 1

a_2 = a_1 + 2

a_3 = a_2 + 3

a_4 = a_3 + 4

So if you go on in this series you will notice that pattern, if you calculate the individual terms and add a_7 and a_8 you can get the answer as B
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