# JavaScript: Composition of operations

Suppose we want to calculate an expression such as `3 * 5 - 2`. That is exactly how we would write it down:

``````console.log(3 * 5 - 2); // => 13
``````

Note that the interpreter performs arithmetic operations in the right order: first division and multiplication, then addition and subtraction. Sometimes we want to change the order of calculations. We'll dig into this topic in the next lesson. Or another example:

``````console.log(2 * 4 * 5 * 10);
``````

As you can see, we can combine operations, which allows us to compute even more complex compound expressions. To visualize how calculations are done inside the interpreter, let's look at an example: `2 * 4 * 5 * 10`.

1. First we calculate `2 * 4` and get `8 * 5 * 10`
2. Then we calculate `8 * 5`, which gives us `40 * 10`
3. Finally, do the last multiplication. The result will be `400`

We can combine operations, making it possible to compute increasingly complex compound expressions.

## Instructions

Write a program that calculates and prints the value of this expression:

``````8 / 2 + 5 - -3 / 2
``````

Don't calculate anything manually, your program should do all the calculations on its own.

The exercise doesn't pass checking. What to do? 😶

• Be sure to attach the test output, without it it's almost impossible to figure out what went wrong, even if you show your code. It's complicated for developers to execute code in their heads, but having a mistake before their eyes most probably will be helpful.
In my environment the code works, but not here 🤨

Tests are designed so that they test the solution in different ways and against different data. Often the solution works with one kind of input data but doesn't work with others. Check the «Tests» tab to figure this out, you can find hints at the error output.

My code is different from the teacher's one 🤔

It's fine. 🙆 One task in programming can be solved in many different ways. If your code passed all tests, it complies with the task conditions.

In some rare cases, the solution may be adjusted to the tests, but this can be seen immediately.

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