Think about what you do when you have a column of twenty numbers and someone asks for the total. You could type =A1+A2+A3+...+A20, hitting every cell by hand. It works, but it is slow, easy to mistype, and painful to fix when the range grows. A built-in function is the shortcut a spreadsheet gives you for exactly this kind of repetitive job: instead of naming every cell, you name the block of cells and tell the spreadsheet what to do with them.
That is the whole idea. A function is a ready-made formula that takes a range of cells and returns a single result — a total, an average, a largest value, and so on. You supply the range; the function does the arithmetic.
The shape of a function
Every function follows the same skeleton:
=FUNCTIONNAME(range)
The = tells the spreadsheet "this is a formula, calculate it." The name says what to do. The parentheses hold what to do it to — usually a range like A1:A10, which means "all cells from A1 down to A10."
So =SUM(A1:A10) reads as: add up everything in the block A1 through A10.
The five functions
| Function | What it returns | Example | Meaning |
|---|
SUM | Total of the values | =SUM(A1:A10) | Adds all numbers in A1:A10 |
AVERAGE | Arithmetic mean | =AVERAGE(A1:A10) | Sum divided by count of numbers |
MAX | Largest value | =MAX(A1:A10) | The biggest number in the range |
MIN | Smallest value | =MIN(A1:A10) | The smallest number in the range |
COUNT | How many numbers | =COUNT(A1:A10) | Counts cells containing numbers |
Take a range holding the marks 45,60,72,38,85.
=SUM(...) gives 300=AVERAGE(...) gives 300/5=60=MAX(...) gives 85=MIN(...) gives 38=COUNT(...) gives 5
Notice AVERAGE is not a separate magic trick — it is SUM divided by COUNT. That relationship is worth holding onto, because it explains the one behaviour that trips up beginners.
AVERAGE divides by the number of numeric cells, not by the number of cells you selected. If a range has 10 cells but only 6 contain numbers, AVERAGE divides the sum by 6, not 10.
The subtlety that catches everyone
COUNT counts only cells that hold numbers. Blank cells and cells containing text are ignored. This is deliberate, and it is what makes AVERAGE behave sensibly: if a student has not yet been given a mark, that empty cell should not drag the average down as if it were a zero.
Suppose the range is 45,60,(blank),38,85. Then:
=SUM(...) =228=COUNT(...) =4 (the blank is skipped)=AVERAGE(...) =228/4=57
If you had wrongly divided by 5, you would get 45.6 — a different, incorrect answer. The blank is not a zero; it is simply absent. …