Question

A farmer knows that a grocery store will reject a shipment of his vegetables if more than 4% of the vegetables contain blemishes. He inspects a large truckload of tomatoes to determine if the proportion with blemishes (p) exceeds 0.04. He selects an SRS of 150 tomatoes from the more than 2,000 tomatoes in the truck. Suppose that 8 tomatoes sampled are found to have blemishes. Which of the assumptions for inference about a proportion is violated, if any?

a. Large Counts: np > 10
b. Large Counts: n(1 – p) > 10
c. The sample is a random sample of the entire population.
d. 10% condition: the sample size is less than 10% of the population.
e. There do not appear to be any violations.

Answer 1

Assumption A is violated

Explanation:

x = number of blemishes = 8

n = sample size = 150

proportion = x/n = 8/150 = 0.0533

1. large counts: np> 10

= 150 * 0.0533 >10

= 7.995 > 10

this assumpton is obviously violated. 7.995 is not greater than 10

2. Large Counts: n(1 - p) > 10

150(1-0.0533)>10

150-7.995 > 10

142.005> 10

there is no violation. The assumption is satisfied

3. This assumption is satisfied. this is because the tomatoes were selected using simple random sampling.

4. 10% of the population = 0.1 * 2000 = 200

the sample size = 150

150 < 200

this assumption is satisfied