Tali is hungry. She sees a vending machine and wants to buy a bag of chips that costs $1.25 and a bottle of water that costs $1.00. Andrew gives her four $1 bills and asks her to buy a bag of chips for him as well. How much is the change? Tali calculates it like this:

total cost: 1.25 x 2 + 1.00 = 3.50 total money: 1.00 x 4 = 4.00 change: 4.00 - 3.50 = 0.50

This is easy enough to do by hand. Tali uses two types of numbers here: integers (like 4) and decimals (like 1.25).

We can also use computer programs to calculate this kind of math problem. With a computer's power, we can do more complicated math very fast. Python uses the number type integer or int to represent integer values and the number type floating-point or float to represent decimal values. The math operations (addition, subtraction, multiplication, and division) are performed by operators using symbols (+, -, *, /). In Python, the multiplication symbol is an asterisk (*) and the division symbol is a forward slash (/). Lastly, the modulus operator (%) gives the remainder of the division. For example, 3 % 7 = 3, because 3 divided by 7 is 0 with remainder 3, and 9 % 7 = 2, because 9 divided by 7 is 1 with remainder 2. Now Let's write a Python program to print out total cost, total money, and change.

The above program is not very efficiently written. Total money and total cost are calculated twice. Can we avoid doing that? Yes - that's why we use variables!

Operators are special symbols that represent computations like addition, subtraction,
multiplication and division. The values the operator works on are called operands.