Question 1025013
Flip a coin has a probability of {{{1/2}}} and it's independent so the probability of the marble problem was,
{{{P=P[m]*(1/2)=(12/40)=3/10}}}
{{{P[m]=3/20}}}
Probability of choosing a white marble from the bag fits the bill. 
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Sherry gets two marks off for not putting her probability in lowest terms though.