Here is the boxplot of the given data:
[1.0, 1.5, 2.5, 3.0, 4.0, 4.0, 4.5, 4.5, 4.5, 4.5, 4.5, 5.0, 5.0, 5.5, 5.5, 5.5, 6.0, 6.0, 6.5, 6.5]
The 5-number summary for this data would be:
Minimum: 1.0
First Quartile (Q1): 2.5
Median: 4.5
Third Quartile (Q3): 5.5
Maximum: 6.5