Answer:
5
Step-by-step explanation:
The interquartile range is the difference between the upper quartile and the lower quartile.
First find the median.
The median is the middle value of the data set arranged in ascending order
1 5 5 7 9 ← data in ascending order
↑ median
The lower quartile is the middle value of the data to the left of the median. If there is not an exact middle then it the average of the values on either side of the middle.
1 5
↑ lower quartile = = 3
The upper quartile is the middle value of the data to the right of the median.
7 9
↑ upper quartile = = 8
Thus
interquartile range = 8 - 3 = 5