The average value of a data set is equal to the sum of each entry divided by the number of entries. In this case, we have 5 scores, so we can find set up the following equation where x is the fifth score:
[tex] \dfrac{78+81+83+76+x}{5} = 81[/tex]
Now solve for x:
[tex] 78 + 81 + 83 + 76 + x = 81(5)[/tex]
[tex]318 + x = 405[/tex]
[tex]x = 87[/tex]
The fifth score must be 87.
