What's the rule for the sequence 1/9,1/3,5/9

The rule for this sequence is that it grows 2/9's each number.

The rule is add 2/5 because 1/3 = 3/9 and 1/9 + 2/9= 1/3 and 1/3 + 2/9 = 5/9

This law is sometimes called the grouping property. as you can see, regardless of how the numbers are grouped, the answer is still 13. the associative law of multiplication is similar to the same law for addition. it says that no matter how you group numbers you are multiplying together, you will get the same answer.