The mean is an average of a set of numbers, where in order to calculate it, we sum all the numbers and divide by the amount of numbers.
For example, in the set {2, 5, 7, 10}, the mean is:
[tex]\frac{2+5+7+10}{4}=\frac{24}{4}=6[/tex]The median is the middle term of the set when it's put in the crescent order.
For example, in the set {4, 7, 2, 10, 5}, the median is:
[tex]\begin{gathered} \text{crescent order}\to\mleft\lbrace2,4,5,7,10\mright\rbrace \\ \text{middle term}\to5 \end{gathered}[/tex]If the number of elements in the set is even, the median will be the average of the two middle terms. For example, in the set {4, 7, 2, 10, 5, 3}, the median is:
[tex]\begin{gathered} \text{crescent order}\to\mleft\lbrace2,3,4,5,7,10\mright\rbrace \\ \text{middle terms}\to4\text{ and 5} \\ \operatorname{median}\to\frac{4+5}{2}=4.5 \end{gathered}[/tex]