This is your answer (x-a).g(a)
1440
because yea
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After the 3rd pick we have: 4 white, 3 red and 8 black marbles.
The probability that the 4th marble is black is:
P ( Black ) = 8 / 15 = 0.5333
After the 4th pick we have: 4 white, 3 red and 7 black marbles.
P ( Red or Black ) = 10 / 14 = 5 / 7 = 0.7143
Total play = 20
Nancy win = 12
Ratio would be: 12/20 = 6/10 = 3/5
So, your answer is 3/5
