Four out of nine, two out of nine, one out of nine, (), one out of 36, () find the law

Four out of nine, two out of nine, one out of nine, (), one out of 36, () find the law

Fill in the blanks: 4 / 9, 2 / 9, 1 / 9, (1 / 18), 1 / 36, (1 / 72)
Analysis: observe the given sequence of numbers and know that each number is the number in front of it multiplied by 1 / 2
1/9×1/2=1/18
1/36×1/2=1/72