I need to calculate some quantiles for a sample of 108 real numbers with unknown mean and unknown variance. I currently store and sort those numbers, but I would try a streaming method where the numbers are not stored. In a paper is written: "If the size of the input stream, N is known, then the following simple algorithm can compute a random sample of size k in one-pass: choose each element independently with probability k/N to include in the sample."; please, could somebody tell me what it means? I need a procedure to retain the best possible accuracy, any suggestion?