A student in the concrete lab, places 6 low strength concrete test cylinders (3500 psi) with a batch of 9 high strength conrete test cylinders (8000 psi): (show all calculations)
a) if a six cylinders are tested what is the probability that 2 are low strength and 4 are high strength?
b) if 5 cylinders are tested what is the probability that all 5 are high strength?