Look at this series: 664, 332, 340, 170, ____, 89, ... What number should fill the blank?

The letters decrease by 1; the numbers are multiplied by 2.

This is a simple addition series with repetition. It adds 3 to each number to arrive at the next, which is repeated before 3 is added again.

Two patterns alternate here. The first pattern begins with 10 and adds 2 to each number to arrive at the next; the alternating pattern begins with 34 and subtracts 3 each time.

In this simple subtraction with repetition series, each number is repeated, then 3 is subtracted to give the next number, which is then repeated, and so on.

Here, there are two alternating patterns. The first begins with 17 and adds 2; the second begins with 32 and subtracts 3.

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

In this series, 5 is added to the previous number; the number 70 is inserted as every third number.

This is a simple alternating addition and subtraction series. The first series begins with 8 and adds 3; the second begins with 43 and subtracts 2.

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.

This is a multiplication series; each number is 3 times the previous number.