Mode: The number that occurs most often in a set of numbers.
To find the mode, first list these numbers in order from least to greatest.
14 - 15 - 18 - 18 - 18 - 18 - 21 - 21 - 24 - 24
Next, look at the list of numbers and identify which number repeats the most in the set. The number 18 occurs 4 times and no other number occurs 4 times or more so our mode for this set of number would be 18.