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%..

 // This function generates 'x' with probability px/100, 'y' with
 // probability py/100  and 'z' with probability pz/100:
 // Assumption: px + py + pz = 100 where px, py and pz lie
 // between 0 to 100
 int random(int x, int y, int z, int px, int py, int pz) {
         // Generate a number from 1 to 100
         int r = rand(, );

         // r is smaller than px with probability px/100
         if (r <= px)
             return x;

          // r is greater than px and smaller than or equal to px+py
          // with probability py/100
         if (r <= (px+py))
             return y;

          // r is greater than px+py and smaller than or equal to 100
          // with probability pz/100
         else
             return z;
 }