Answer:
12
Explanation:
The interquartile range is the difference between the upper quartile and the lower quartile.
Firstly find the median of the data.
The median is the middle value of the data arranged in ascending order. If there is no exact middle value then it is the average of the values either side of the middle.
5, 6, 13, 18, 18 ← data in ascending order
↑ middle value
median = 13
The upper quartile Q₃ is the middle of the data to the right of the median
13, 18, 18
↑ middle value
Q₃ = 18
The lower quartile Q₁ is the middle value of the data to the left of the median
5, 6, 13
↑ middle value
Q₁ = 6
Interquartile range = Q₃ = Q₁ = 18 - 6 = 12