A computer security expert is investigating a particularly dangerous strain of malware. She determines that the malware has approximately a 42% chance of infecting a typical computer setup. Her company knows that 30 of its computers were exposed to the malware. a. If possible, using a normal approximation of the binomial distribution, find the probability that:

1. none of the computers were infected;

2. all of the computers were infected;

3. exactly 10 computers were infected;

4. more than 20 computers were infected.