Final answer:
The prevalence of peptic ulcer disease can be calculated by dividing the number of cases by the total population and multiplying by 1000.
Step-by-step explanation:
The prevalence of peptic ulcer disease can be calculated by dividing the number of cases by the total population and multiplying by 1000.
In this case, there were 90 cases of peptic ulcer disease among a population of 9000. To calculate the prevalence, divide 90 by 9000 and then multiply by 1000:
Prevalence = (90/9000) x 1000 = 10 per 1000 people
Therefore, the prevalence of peptic ulcer disease in this population is 10 cases per 1000 people.