---
title: "p chart"
author: ""
date: ""
output: html_document
---

Production of skrews with mean diameter 10mm is allowed to vary in the
interval 9.9mm-10.1mm. Each day a sample of 3000 is taken and the
number of skrews not fulfilling the specification is counted.

The numbers of defectives for the last 20 days is:

```{r}
x <- c(30,40,33,40,39,56,52,54,35,44,40,41,49,43,63,65,70,70,67,64)
```

Identify a point in time where you suspect, that a change has taken
place.

Use the data before this point to calculate the limits of a 3*sigma
p-chart.

Is there an indication of a change?