Tiana is a quality controller in a clothes factory. She checks for four possible types of defects in shirts.
Of the shirts with defects, the proportion of each type of defect is as shown in the table below.
| Type of defect | Colour | Fabric | Sewing | Sizing |
| Probability | 0.25 | 0.30 | 0.40 | 0.05 |
Shirts with defects are packed in boxes of 30 at random.
- Find the probability that:
- a box contains exactly 5 shirts with a colour defect
[2 marks]
- a box contains fewer than 15 shirts with a sewing defect
[2 marks]
- a box contains at least 20 shirts which do not have a fabric defect.
[3 marks]
- Tiana wants to investigate the proportion, \(p\), of defective shirts with a fabric defect.
She wishes to test the hypotheses
H\(_0\): \(p = 0.3\)
H\(_1\): \(p < 0.3\)
She takes a random sample of 60 shirts with a defect and finds that \(x\) of them have a fabric defect.
- Using a 5\% level of significance, find the critical region for \(x\).
[5 marks]
- In her sample she finds 13 shirts with a fabric defect.
Complete the test stating her conclusion in context.
[2 marks]