How to deal with the principle of stealing red envelopes

The principle of stealing red envelopes
Want to use PHP to achieve the function of red envelopes, who send the more red envelopes, Rob more, do not know if what algorithm appropriate
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I think of a way of thinking I do not know the appropriate (Novice mo spray)
Set up two random numbers, say one is 0-100 random to how much to give red envelopes such as this number is 1-10 corresponding to get red envelopes, your probability is 10%
Another random number range 0-50 randomly get a number such as also 1-10 corresponds to get red envelopes so the probability is 20% opposite;
Whether it's the first or the second, according to the TOP10 in the database.
That's just my idea.
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You'll record the number of red envelopes each person sends (amount)
So you will know the number of red envelopes (amount) of a person, the proportion of the total number of red envelopes (amount)
According to this proportion can meet who sent the more red envelopes, Rob also more requirements

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