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Let’s say we are writing a program that represents a user’s bank account. With variables, we know how to store a balance! We’d use a `double`, the primitive type that can hold big decimal numbers. But how would we deposit and withdraw from the account?

Lucky for us, we have the ability to manipulate the value of our variables. We can use expressions, arithmetic operators, and more in order to change our variables’ values.

For example, Java has built-in arithmetic operations that perform calculations on numeric values:

``````// declare initial balance
double balance = 20000.99;
// declare deposit amount
double depositAmount = 1000.00;
// store result of calculation in our original variable
balance = balance + depositAmount;``````

In the final line of the code above, we used the expression `balance + depositAmount` to determine the new value of the `balance` variable. When an expression is executed, it produces a single value.

The data type of a variable plays a large role in the operations we can use to manipulate it. We can think of a data type as a combination of a set of values, and a set of operations on those values. For example, the `double` data type is comprised of values like `4.8` and operations like addition (`+`). For now, we’ll mainly focus on the set of operations that can be used on numbers and booleans.

The data type of an expression is determined by the resulting value. For example, an expression that uses two `int` values will evaluate to an `int` value. If an expression contains a `double` value, then the resulting value will also be type `double`.

Throughout this lesson, we will learn how to manipulate variables of different data types.

### Instructions

1.

In the file GuessingGame.java, we have defined two integers `mystery1` and `mystery2`.

We will talk about these operators, among others, in the rest of the lesson.

Use `System.out.println()` to print the variable that holds a value of `2`.