Question

How to generate random numbers which will provide proper results on division (i.e the results should round to exactly 1 or 2 places after the decimal point).

(e.g a whole number by a decimal number providing decimal results – I have given a set of sample inputs below)

2827 by 2.5 = 1130.8
1747 by 0.8 = 2183.75
425 by 0.4 = 1062.5
935 by 0.8 = 1168.75

Answer 1

It is worth noting that all integers can be divided by 0.4, 0.8 or 2.5 and be represented to two decimal places. This is because it is the same as multiplying by 2.5, 1.25, and 0.4

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However, if you have a divisor for which this is not true, you can do this in a loop.

double divisor = 2.4;
double factor = 100/divisor;
Random rand = new Random();
int maxValue = 1000;
double ERROR = 1e-14*maxValue;

for(int i=0;i<100;i++) {
long randNum;
do {
   randNum = rand.nextInt(maxValue+1);
    if (Math.abs(randNum * factor - (long) (randNum * factor)) > ERROR)
        System.out.println("reject "+randNum + " => "+randNum/divisor);
} while(Math.abs(randNum * factor - (long) (randNum * factor)) > ERROR);
System.out.println(randNum + " => "+randNum/divisor);

prints

729 => 303.75
285 => 118.75
84 => 35.0
123 => 51.25
999 => 416.25
75 => 31.25
reject 727 => 302.9166666666667
reject 842 => 350.83333333333337
504 => 210.0
reject 368 => 153.33333333333334
441 => 183.75
579 => 241.25
165 => 68.75

This will generate random numbers until you have a number which is a multiple of 0.01.