Answer: XVII

Explanation:
This is a simple addition series; each number is 3 more than the previous number.

Answer: IV

Explanation:
This is an alternating addition and subtraction series. Roman numbers alternate with Arabic numbers. In the Roman numeral pattern, each number decreases by 1. In the Arabic numeral pattern, each number increases by 1.

Answer: 15

Explanation:
In this simple addition with repetition series, each number in the series repeats itself, and then increases by 12 to arrive at the next number.

Answer: 13

Explanation:
Two series alternate here, with every third number following a different pattern. In the main series, 3 is added to each number to arrive at the next. In the alternating series, 5 is subtracted from each number to arrive at the next.

Answer: W26

Explanation:
In this series, the letters progress by 1; the numbers decrease by 3.

Answer: 15 12

Explanation:
This is an alternating addition and subtraction series, in which the addition of 4 is alternated with the subtraction of 3.

Answer: 20 21

Explanation:
Here, there are two alternating patterns, with every other number following a different pattern. The first pattern begins with 13 and adds 2 to each number to arrive at the next; the alternating pattern begins with 29 and subtracts 3 each time.