Question

Julia owns 13 books. She buys two new books every week. Which arithmetic sequence describes the number of books she has?
A. a1=13;an=an−1+2
B. a1=2;an=an−1+13
C. a1=13;an=an+1+2
D. a1=2;an=an+1+13

Answer 1

A. a1 = 13; an = a_{n−1} + 2

Reason: start with 13 books (a1 = 13) and each week adds 2, so each term is the previous term plus 2. (Explicitly an = 13 + 2(n−1).)