A number theory problem by A Former Brilliant Member

Number Theory Level pending

A box contains 12 identical marbles. Five are brown and seven are not. Marvin is blindfolded and selects two marbles. What is the probability that Marvin selects at least one brown marble?

7/22 15/22 8/22 16/22

A Former Brilliant Member by A Former Brilliant Member

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1 solution

Probability that Marvin doesn't select brown marble, 7 12 \frac{7}{12} ∗ * 6 11 \frac{6}{11} = = 7 22 \frac{7}{22}

Probability that at least one marble is brown, 1 − 1- 7 22 \frac{7}{22} = = 15 22 \frac{15}{22}

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