I need to know how to generate a stand alone random number in a survey and use that number in an equation.

You can learn that from the examples.

manual.limesurvey.org/Expression_Manager...e_Question_Per_Group

I don't want to randomize my questions, I want to create a random number to be multiplied in an hidden equation . for example (arrival time * cost / random number between 1 and 4) how can I do that ??

As I said you can learn that from these examples. You can see the usage of rand in the example. rand Generate a random integer, see this example int rand() OR int rand(min, max)
Short Example:
You can create a equation question with the name "randnumber" and place this ExpressionScript inside the question. That creates a stable randomnumber between 1 and 4
With stable I mean the checking for an value via if clause. Rand is triggered every time a survey respondent is reaching the random question. That behaviour is mostly not wanted cause the number would changes during a survey visit. I recommend to create randomnumber at the beginning of the survey and use the variables inside other equations as you like.

 

Thank you this code is so helpful, one last question
if I want to use the same code but to generate rand number between 0 & 1
with decimals example "0.43223" how would the could change I tired making it "{if(is_empty(randnumber),rand(),randnumber.NAOK)}" but it did not work thank you!!

The rand() function only generates integers.
www.php.net/manual/en/function.rand.php

You will probably have to do something like this:
stackoverflow.com/questions/10419501/use...eteween-two-decimals