The standard deviation of the given data $[12, 18, 26, 27, 28]$, rounded to one decimal place, is $6.9$.

Would you like further details on the calculation? Here are 5 related questions for further exploration:

1. How is the variance related to the standard deviation?
2. What is the difference between population and sample standard deviation?
3. How would adding an outlier affect the standard deviation?
4. Can you calculate the mean for the given data set?
5. How is standard deviation used in real-world data analysis?

Tip: Standard deviation measures how spread out the data is from the mean. A higher value indicates more variability.