RS Aggarwal Solutions for Class 9 Chapter 18 “Mean-median-and-mode-of-ungrouped-data”, the mean (average) of a data set is found by adding all numbers in the data set and then dividing by the number of values in the set. The median is the middle value when a data set is ordered from least to greatest. The mode is the number that occurs most often in a data set. Median of an Ungrouped Data Set, the median refers to the middle data point of an ordered data set at the 50% percentile. If a data set has an odd number of observations, then the median is the middle value. If it has an even number of observations, the median is the average of the two middle values. This Chapter contains problems and formulas which are used in finding mean, median and mode of ungrouped data.