Determine the type of distribution and the best measure of center and spread of the data set.
$$1,7,12,15,17,18,18,20,21,21,24,27$$

The distribution is so $\mathrm{\nabla }=◻$ and $=◻$ best represent the data set.
(Type integers or decimals rounded to the nearest tenth as needed.)

Step 1 ：First, we need to determine the type of distribution. This can be done by plotting the data and observing its shape. If the data is symmetric, it is a normal distribution. If the data is skewed to the right or left, it is a skewed distribution.

Step 2 ：Next, we need to determine the best measure of center and spread. For a normal distribution, the best measure of center is the mean and the best measure of spread is the standard deviation. For a skewed distribution, the best measure of center is the median and the best measure of spread is the interquartile range.

Step 3 ：Let's start by plotting the data to determine the type of distribution. The histogram shows that the data is slightly skewed to the right. Therefore, the distribution is skewed.

Step 4 ：Next, let's calculate the median and interquartile range as they are the best measures of center and spread for a skewed distribution. The median is $\boxed{{\displaystyle 18.0}}$ and the interquartile range is $\boxed{{\displaystyle 6.75}}$.

Step 5 ：Final Answer: The distribution is skewed and the median and interquartile range best represent the data set. Therefore, the final answer is $\boxed{{\displaystyle 18.0}}$ and $\boxed{{\displaystyle 6.75}}$.