2. A study surveys a random sample of 3000 school children from the population of South Yorkshire. On the day of the survey 21 of them report that they have head lice. Therefore the prevalence of head lice is:

a) (3000/21)/100 = 1.42%

b) (21/3000) × 100 = 0.7%

c) (3000 + 21)/1000 = 3.0%

d) (100/3000) + 21 = 21.0%