For each of the following, write out null and the alternative hypotheses, being sure to indicate whether the alternative is one-sided or two-sided.
a) Consumer Repons discovered that 20% of a certain computer model had warranty problems over the first three months. From a random sample, the manufacturer wants to know if a new model has improved that rate.
b) The last time a philanthropic agency requested donations, 4.75% of people responded. From a recent pilot mailing, they wonder if that rate has increased.
c) A student wants to know if other students on her campus prefer Coke or Pepsi.