In an investigation to determine the effect of the plant growth substance indole-3-acetic acid (IAA) on cell elongation, ten oat coleoptile segments were incubated in distilled water (Control) and another ten coleoptile segments of the same initial length were incubated in a solution of IAA (Treated). The percentage increase in the length of each coleoptile segment over 24 hours was recorded. The results are shown in the table below:

$$\begin{array}{ccc}Coleoptile\; segment& Control\; growth\; (\%)& IAA\; Treated\; growth\; (\%)\\ 1& 12.4& 25.2\\ 2& 12.1& 24.8\\ 3& 12.5& 25.4\\ 4& 12.2& 25.0\\ 5& 12.6& 24.6\\ 6& 12.3& 4.2\\ 7& 12.4& 25.1\\ 8& 12.2& 24.9\\ 9& 12.5& 25.3\\ 10& 12.3& 24.7\\ Average& 12.4& ?\end{array}$$