Solution: This is a simple division series; each number is one-half of the previous number.
In other terms to say, the number is divided by 2 successively to get the next result.
4/2 = 2
2/2 = 1
1/2 = 1/2
(1/2)/2 = 1/4
(1/4)/2 = 1/8 and so on.

Solution: This is a simple alternating addition and subtraction series. In the first pattern, 3 is added; in the second, 2 is subtracted.

Solution: This is an alternating number subtraction series. First, 2 is subtracted, then 4, then 2, and so on.

Solution: In this simple alternating subtraction and addition series; 1 is subtracted, then 2 is added, and so on.

Solution: In this series, each number is repeated, then 13 is subtracted to arrive at the next number.

Solution: In this alternating repetition series, the random number 21 is interpolated every other number into an otherwise simple addition series that increases by 2, beginning with the number 9.

Solution: This is a simple subtraction series. Each number is 6 less than the previous number.

Solution: This alternating addition series begins with 3; then 1 is added to give 4; then 3 is added to give 7; then 1 is added, and so on.

Solution: This is a simple addition series with a random number, 8, interpolated as every other number. In the series, 6 is added to each number except 8, to arrive at the next number.

Solution: This is a simple alternating subtraction series, which subtracts 2, then 5.