Final answer:
In statistics, standardized data always has a mean of 0 and a standard deviation of 1. In a left-skewed distribution, the median will exceed the mean, and the sum of deviations around the mean is always zero. However, the mean cannot be directly observed on a box plot.
Step-by-step explanation:
The statement concerning the mean is an aspect of descriptive statistics, particularly in the context of understanding the properties of a normal distribution and other types of distributions. The statement 'standardized data will always have a mean of 0 and a standard deviation of 1' is true. This is the defining property of a z-score, which is a measure used in standard normal distributions. Moreover, 'in a left-skewed distribution, we expect that the median will exceed the mean' is correct because in a negatively skewed distribution, the mean tends to be less than the median. Lastly, 'the sum of the deviations around the mean is always zero' is a fundamental property of the mean in any distribution. However, the statement 'the value of the mean can clearly be seen on a box plot' is not true, as a box plot displays the median, not the mean.