# Introduction to Statistics and Data Analysis | Probability & Statistics for Engineers & Scientists | Walpole | Problem 1.3

A certain polymer is used for evacuation systems for aircraft. It is important that the polymer be re­sistant to the aging process. Twenty specimens of the polymer were used in an experiment. Ten were assigned randomly to be exposed to the accelerated batch aging process that involved exposure to high tempera­tures for 10 days. Measurements of the tensile strength of the specimens were made and the following data were recorded on tensile strength in psi.

 No aging: 227 222 218 217 225 218 216 229 228 221 Aging: 219 214 215 211 209 218 203 204 201 205

(a) Do a dot plot of the data.

(b) From your plot, does it appear as if the aging pro­cess has had an effect on the tensile strength of this polymer? Explain.

(c) Calculate the sample mean tensile strength of the two samples.

(d) Calculate the median for both. Discuss the simi­larity or lack of similarity between the mean and median of each group.

#### Solution:

Part a

A dot plot is shown below.

In the ﬁgure, “×” represents the “No aging” group and “◦” represents the “Aging” group.

Part b

Yes; tensile strength is greatly reduced due to the aging process.

Part c

$\displaystyle Mean_{aging}=209.90$ and $\displaystyle Mean_{No\:aging}=222.10$

Part d

$\displaystyle Median_{Aging}=210$ and $\displaystyle Median_{No\:Aging}=221.50$.

The means and medians for each group are similar to each other.