Question 16.17

16.17 Polyester fabrics in landfills.

How quickly do synthetic fabrics such as polyester decay in landfills? A researcher buried polyester strips in the soil for different lengths of time, then dug up the strips and measured the force required to break them. Breaking strength is easy to measure and is a good indicator of decay. Lower strength means the fabric has decayed. Part of the study involved burying 10 polyester strips in well-drained soil in the summer. Five of the strips, chosen at random, were dug up after two weeks; the other five were dug up after 16 weeks. Here are the breaking strengths in pounds:6

poly

2 weeks 118 126 126 120 129
16 weeks 124 98 110 140 110
  1. Make side-by-side stemplots for the two groups. Does it appear reasonable to assume that the two distributions have the same shape?
  2. Is there evidence that breaking strengths are lower for strips buried longer?

16.17

(a) The distributions are very different and not the same shape. (b) From software, The data do not show a systematic difference in breaking strengths.