Workers in silicon factories are prone to a lung disease called silicosis. In a recent survey in a factory, about \(11 \%\) of the workers have been infected by it. Assume the same rate of infection holds everywhere. Use the normal distribution to approximate the probability that, out of a random sample of 425 workers, the numbers that are prone to infection at present will be

(a) 30 or more;

(b) 28 or less.