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Cumulative probability question


I have been experimenting with Mathematica in order to receive answers 
to my problem, so far without success. I have tried various forms of CDF 
and HypergeometricDistribution, but I seem to not know the proper 
addressing of the parameters for the problem.

The problem itself is the following (with numbers given for a more 
illustrative example): Given an urn containing N(=70) items in total, 
of which n(=4) are marked, we want to draw i(=2) or more marked 
items.

a) What is the formula describing the number of draws required to 
succeed in drawing at least i items with a probability of at least 50%?
b) How do you make a graph of the probability (of drawing at least i 
items) graphed against the number of draws?
c) What are the equations that need to be solved to get a numerical 
answer on a) and b)?

Thank you for your assistance in advance
P=E9ter Sis=E1k




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