This is an alternating addition series with a random number, 4, interpolated as every third number.

Correct Option: D

This is an alternating addition series with a random number, 4, interpolated as every third number. In the main series, 1 is added, then 2 is added, then 1, then 2, and so on.

This is an alternating subtraction series with repetition. There are two different patterns here. In the first, a number repeats itself; then 3 is added to that number to arrive at the next number, which also repeats.

Correct Option: E

This is an alternating subtraction series with repetition. There are two different patterns here. In the first, a number repeats itself; then 3 is added to that number to arrive at the next number, which also repeats. This gives the series 17, 17, 20, 20, 23, and so on. Every third number follows a second pattern, in which 3 is subtracted from each number to arrive at the next : 34, 31, 28.

This alternating addition series begins with 3; then 1 is added to give 4;

Correct Option: D

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.

This is a simple alternating subtraction series,

Correct Option: A

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

In this alternating repetition series, the random number 21 is interpolated every other number into an otherwise

Correct Option: C

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.