Sort the list of numbers in running order. The middle one is the median, also called the second quartile, Q2.
When having an even number of results, there are two middle numbers, and the median is the average of the two results.
Divide the sorted list into two lists. If the original list is odd, you may insert the median to both lists.
Q1, the lower quartile, is the median of the left list.
Q3, the upper quartile, is the median of the right list.
Interquartile range (IQR) is the difference between the upper quartile and the lower quartile. IRQ = Q3 - Q1.
Accumulate the sum of all the values, and then divide the result by the total count of values.
Count the total number of time each value appears in the list. The value appears most times is the mode.
You may get more than one mode, as several values may have the same frequency.
For a sample from a continuous distribution, you may need to group the values into equal intervals, and the mode will be the interval with the highest frequency.
Since no single value repeats, you may find the mode in the group level histogram