Probability | mn coins distributed equally in m purses | The chance that 2 coins r in the same purse

Probability | mn coins distributed equally in m purses having n coins each. Find the chance that two specified coins will be found in the same purse. What the chances become when r purses are examined and found not to contain either coin.

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[chandrasekhar]

Sir in part 1 of this question, the "A" coin can be any of the m purses. So won't the probability be m×[(n-1) ÷ (mn-1)]?

[anandjaiswal]

Sir is this lecture focused on jee advanced