# What is the product of 21% and some number?

$.21 x$, where $x$ is some number.
The first step is figuring out what 21% is as a number. Well, 21% means 21 parts out of a 100 - which can be expressed as the fraction $\frac{21}{100}$. We could leave it like this, but decimals are easier on the eyes than fractions. To convert $\frac{21}{100}$ to a decimal, all we do is divide, getting $.21$.
Next, we interpret "the product of 21% and some number". What is some number? The answer is in the question! Some number is any number - a decimal, fraction, number, square root, etc, etc. To represent "some number" in math terms, we use a letter called a variable. This variable just stands for some number - it can be anything you want it to be. Usually, variables are something like $n$, $x$, and $y$. We'll use $x$ because that's the most common one.
Now, what does "product" mean? Multiplication! It's that easy. So the product of 21% ($.21$) and some number ($x$) is $.21$ multiplied by $x$, or $.21 x$.