Question: 1- The mode, median and mean tell us something about a set of observations. The mode is the only measure of center appropriate for nominal data. For example, if we were looking at the most frequently purchased food item in a certain snack bar in 1999, it make sense to say that the most frequent (modal) food purchased was mini chocolate. The median is at the middle of an ordered data set and is a useful measure for ordinal variables, while the mean only makes sense for interval and ratio scales of measurement
2- A populationis is a set of persons or objects that has a common observable characteristics and a complete set of items that share at least one property in common that is the subject of a statistical analysis. An example is the people in certain locality that share a common geographic origin, language, literature, and genetic heritage, among other traits, that distinguish them from people of different nationalities.
3- The mean is the summary of an entire population. Sometimes it is called the average. It isn't a particular individual, but rather the entire population (University, 2013). The mean could be used to determine the average age of a population. If you add all the ages of all the people in the population and divide by the number of individuals, it would give you the mean. This is the "summary" of the population. The median is more centralized and would be used to explain what a "typical, normal, or average" member of the population is (University, 2013). You could use the median to again find the median age. This is slightly different than the mean in the way that there is only 1 answer. The median is the middle of the data set (University, 2013), meaning it may be slightly higher or lower than the mean. Sometimes outliers will skew the numbers, but it isn't affected as much as the mean would be. The mode is used to calculate the number that appears the most in a set of numbers. Going along with the ages of the individuals, we would write out all ages of the individuals in the community. If the age of 60 showed up 18 times and was the highest amount of all the numbers, the mode would be 60. The mode is not used very often because it is not a measure of the centre of the data in the same way that the median and mean can be.
Reference: University of Wollongong. (2013, August 12). Appropriate use of mean, median and mode.