Question

A box contains 15 green marbles and 16 white marbles. If the first marble chosen was a white marble, what is the probability of choosing, without replacement, another white marble

Answer 1

Answer: 8/31

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Step-by-step explanation:

16/31 represents the probability of picking a white marble

This is because there are 16 white out of 15+16 = 31 total.

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After we make a first selection, we have 16-1 = 15 white marbles left out of 31-1 = 30 marbles overall. The probability of selecting another white marble is 15/30 = 1/2.

Multiply those two fractions:

(16/31)*(1/2) = (16*1)/(31*2) = (2*8)/(31*2) = 8/31

which represents the probability of selecting two white marbles in a row, such that we don't put the first one back (and there's no replacement).