Answer
a)0.899
b)0.00493
Work Step by Step
a) We know that $probability=\frac{number \ of \ good \ outcomes}{number\ of\ all\ outcomes}$, hence $probability=\frac{2518-252}{2520}=0.899.$
b)Two events are dependent, if the outcome of one effects the outcome of the other. Here the events are independent, because the sampling was done with replacement, also $probability=\frac{number \ of \ good \ outcomes}{number\ of\ all\ outcomes}$, hence $probability=\left (\frac{2518-252}{2520}\right )^{50}=0.00493.$
