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Generate a random number between

and
.

Include numbers after the decimal point.

var randomnumber = Math.floor(Math.random() * (maximum - minimum + 1)) + minimum;

Why use `Math.floor()` and not `Math.round()`?
As an example, let's say that you want to generate numbers in
the range of 0 to 2.
If you do `Math.round(0.4)` you get 0, and if you do
`Math.round(0.5)` you get 1.
On the other end of your random range, if you do `Math.round(1.4)`
you get 1, and if you do `Math.round(1.5)` you get 2.

But this means that you are half as likely of getting 0 and 2 as you
are of getting 1. Look at this number line:

| 0 | 1 | 2 | 0.0-0.1-0.2-0.3-0.4-0.5-0.6-0.7-0.8-0.9-1.0-1.1-1.2-1.3-1.4-1.5-1.6-1.7-1.8-1.9-2.0

Notice that the space for 0 and 2 is smaller than the space for 1.
If you wanted to have an equal chance of getting 0, 1, and 2 using
`Math.round()`, you would have do some manipulation with decimal
numbers in your random number formula. However, there is an easier way.

If you use `Math.floor()` on numbers like 0.4, 1.4, and 2.4 for
example, this is the number line that you get:

| 0 | 1 | 2 | 0.0-0.1-0.2-0.3-0.4-0.5-0.6-0.7-0.8-0.9-1.0-1.1-1.2-1.3-1.4-1.5-1.6-1.7-1.8-1.9-2.0-2.1-2.2-2.3-2.4-2.5-2.6-2.7-2.8-2.9

As you can see, each of the three numbers in the 0 to 2 range has the same
amount of space on this number line, making each one equally likely when you
put a random number into `Math.floor()`.

Page last updated 2014-04-10T16:46:50-05:00