A manufacturer claims 90% of products pass inspection. A sample of 200 products has 170 passing. Test whether the true rate is less than 90%.
What is the test statistic z?
- A
−1.41
- B
−2.50
- C
−1.96
- Dcheck_circle
−2.36
Explanation
p̂ = 170/200 = 0.85. SE₀ = sqrt(0.9·0.1/200) = 0.0212. z = (0.85 − 0.90)/0.0212 ≈ −2.36.