Question

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?

Answer 1

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.