How to make 5 random numbers with sum of 100

Question

do you know a way to split an integer into say... 5 groups. Each group total must be at random but the total of them must equal a fixed number.

for example I have \"

Answer 1

I have a slightly different approach to some of the answers here. I create a loose percentage based on the number of items you want to sum, and then plus or minus 10% on a random basis.

I then do this n-1 times (n is total of iterations), so you have a remainder. The remainder is then the last number, which isn't itself truley random, but it's based off other random numbers.

Works pretty well.

/**
 * Calculate n random numbers that sum y.
 * Function calculates a percentage based on the number
 * required, gives a random number around that number, then
 * deducts the rest from the total for the final number.
 * Final number cannot be truely random, as it's a fixed total,
 * but it will appear random, as it's based on other random
 * values.
 * 
 * @author Mike Griffiths
 * @return Array
 */
private function _random_numbers_sum($num_numbers=3, $total=500)
{
    $numbers = [];

    $loose_pcc = $total / $num_numbers;

    for($i = 1; $i < $num_numbers; $i++) {
        // Random number +/- 10%
        $ten_pcc = $loose_pcc * 0.1;
        $rand_num = mt_rand( ($loose_pcc - $ten_pcc), ($loose_pcc + $ten_pcc) );

        $numbers[] = $rand_num;
    }

    // $numbers now contains 1 less number than it should do, sum 
    // all the numbers and use the difference as final number.
    $numbers_total = array_sum($numbers);

    $numbers[] = $total - $numbers_total;

    return $numbers;
}

This:

$random = $this->_random_numbers_sum();
echo 'Total: '. array_sum($random) ."\n";
print_r($random);

Outputs:

Total: 500
Array
(
    [0] => 167
    [1] => 164
    [2] => 169
)