How many integers in the following infinite series are positive: 100, 91, 82, 73 . . . ?

The first and fourth terms of an arithmetic sequence are, respectively,

and

.

Which of the following is the common difference of the sequence?

The first term of an arithmetic sequence is 20; the tenth term is 100. What is the sixteenth term?

An arithmetic sequence has as its first term 17. Its tenth term is . What is the sum of its second and ninth terms?

In a sequence of numbers, each term is times larger than the one before it. If the 3rd term of the sequence is 12, and the 6th term is 96, what is the sum of all of the terms less than 250?

Which of the following are not natural numbers?

I. 1

II. 0

III. 349010

IV. -2

V. 1/4