8.5 A random sample of six salespeople who attended a motivational course on sales techniques was monitored 3 months before and 3 months after the course.

The table shows the values of sales (in thousands of euros) generated by these six salespeople in the two periods. Assume that the population distributions are normal. Find an 80% confidence interval for the difference between the two population means.

Salesperson Before the Course After the Course 1 210 235 2 289 301 3 212 196 4 327 340 5 163 191 6 205 194