If `NaN`

pops up unexpectedly, there's probably an error in your math. One way to debug math errors is by evaluating expressions piece by piece. For example:

```
int students = 10 * 10;
int tables = 4 / 4 - 1;
int studentsPerTable = students / tables;
System.out.println("studentsPerTable is " + studentsPerTable); // prints NaN
```

Let's go through all the variables:

```
System.out.println("students is " + students);
"students is 100"
System.out.println("tables is " + tables);
"tables is 0" // Ah ha!
```

If we look at the line that declared the `tables`

variable again:

```
int tables = 4 / 4 - 1;
```

Oops – we missed a set of parentheses, and it should've been:

```
int tables = 4 / (4 - 1);
```