A consumer magazine wants to compare lifetimes of ballpoint pens of three different types. The magazine takes a random sample of pens of each time and records the lifetimes (in minutes) in the table below. Do the data indicate that there is a difference in the mean lifetime for the three brands of ballpoint pens?

The first step would be to look at the average for each brand.

The average can be calculated as:

A = (a1 + a2 + + an)/N

where a1 is the first lifetime, a2 is the second one, etc. And N is the total number of data points.

So, for Brand 1 we have:

A1 = (260 + 218 + 184 + 219)/4 = 220.25

Brand 2:

A2 = (181 + 240 + 162 + 218)/4 = 200.25

Brand 3:

A3 = (238 + 257 + 241 + 213)/4 = 237.25

So only from this, we can see that Brand 3 has the larger lifetime, then comes Brand 1 and last comes Brand 2.