How to efficiently generate five numbers that add to one? I have access to a random number generator that generates numbers from 0 to 1. Using this, I want to find five random numbers that add up to 1.
How can I do this using the smallest number of steps possible?
Edit: I do want the numbers to be uniformly distributed.
 A: To expand on the comment made by Zev Chonoles, it is trivial to show that given $5$ random numbers, $x_{1},\dots,x_{5}\in\mathbb{R}$, you can scale them to add up to one:
$$\frac{x_{1}}{\sum_{i=1}^{5}x_{i}}+\cdots+\frac{x_{5}}{\sum_{i=1}^{5}x_{i}}=1$$
If we multiply both sides of the equation by $\sum_{i=1}^{5}x_{i}=x_{1}+\cdots+x_{5}$, we get:
$$x_{1}+\cdots+x_{5}=\sum_{i=1}^{5}x_{i}$$
Which is true by definition. Q.E.D.
A: This can be done with the following strategy. 
Generate $X \sim \textrm{Unif}[0,{2 \over 5}].$ Let $Y = {2 \over 5} - X.$ Generate $Z \sim \textrm{Unif}[0,{2 \over 5}].$ Set $W = V = {3 \over 10} - {Z \over 2}.$ 
With this set up, we know that $X + Y + Z + W + V = 1$ as required. And each random variable has a uniform distribution, although not all have the same uniform distribution. 
The accepted solution does not generate uniform random variables. For example, consider the first point $x_1$ of that proposed method. It is the minimum of four Unif$[0,1]$ random variables. The minimum of uniform random variables does not have a uniform distribution.  
A: Here is a way to satisfy the basic requirements of the question and have all of the component random variables identically uniformly distributed. Generate $V$ as uniform$[0,{2 \over 5}].$ Let $$W = \begin{cases} V+{1/10} \ , & \text{if} \ V \le {3/10} \\ V-{3/10} \ , & \text{if} \ V \gt {3/10} \end{cases}$$ Let $$X = \begin{cases} V+{2/10} \ , & \text{if} \ V \le {2/10} \\ V-{2/10} \ , & \text{if} \ V \gt {2/10} \end{cases}$$ Let $$Y = \begin{cases} V+{3/10} \ , & \text{if} \ V \le {1/10} \\ V-{1/10} \ , & \text{if} \ V \gt {1/10} \end{cases}$$ Let $$Z = 1-V-W-X-Y.$$ This may not be the best approach, but it does require only one generation of a uniform random variable since $W, X, Y,$ and $Z$ are all dependent on $V.$ 
