Write a function that generates one of 3 numbers according to given probabilities

You are given a function rand(a, b) which generates equiprobable random numbers between [a, b] inclusive. Generate 3 numbers x, y, z with probability P(x), P(y), P(z) such that P(x) + P(y) + P(z) = 1 using the given rand(a,b) function.
The idea is to utilize the equiprobable feature of the rand(a,b) provided. Let the given probabilities be in percentage form, for example P(x)=40%, P(y)=25%, P(z)=35%..

 1 // This function generates 'x' with probability px/100, 'y' with 

 2 // probability py/100  and 'z' with probability pz/100:

 3 // Assumption: px + py + pz = 100 where px, py and pz lie 

 4 // between 0 to 100 

 5 int random(int x, int y, int z, int px, int py, int pz) {       

 6         // Generate a number from 1 to 100

 7         int r = rand(1, 100);

 8       

 9         // r is smaller than px with probability px/100

10         if (r <= px)

11             return x;

12  

13          // r is greater than px and smaller than or equal to px+py 

14          // with probability py/100 

15         if (r <= (px+py))

16             return y;

17  

18          // r is greater than px+py and smaller than or equal to 100 

19          // with probability pz/100 

20         else

21             return z;

22 }