Answer:
About 1677 people in the county will have blood-type A−.
Explanation:
From the question, 12 out of 245 patients have blood-type A−.
To estimate the number of people in the county which has a population of 34,237 people with blood-type A−, we will assume that for every 245 people out of the 34,237 people, 12 of them have blood-type A−.
Let the number of people with blood-type A− in the county be x.
Now,
If 12 people out of 245 people have blood-type A−
Then, x people out of 34237 people will have blood-type A−
245 × x = 34237 × 12
245x = 410844
x = 410844/245
x = 1676.9
x ≅ 1677
Hence, about 1677 people in the county will have blood-type A−.