A group of researchers investigated the effect of the plant hormone gibberellin on stem elongation in a dwarf variety of pea plants (Pisum sativum). They treated six different plants at each of four different concentrations of gibberellin and measured the internode length of the primary shoot after 10 days. Their results are shown in the table below.
| Gibberellin concentration (mg dm−3\text{mg dm}^{-3}mg dm−3) | Plant 1 internode length (mm) | Plant 2 internode length (mm) | Plant 3 internode length (mm) | Plant 4 internode length (mm) | Plant 5 internode length (mm) | Plant 6 internode length (mm) | Mean internode length (mm) |
|---|---|---|---|---|---|---|---|
| 0.0 (Control) | 12.1 | 12.8 | 11.9 | 13.0 | 12.4 | 12.8 | 12.5 |
| 1.0 | 17.8 | 18.5 | 17.9 | 18.4 | 18.1 | 18.9 | 18.3 |
| 5.0 | 24.6 | 25.9 | 24.1 | 26.3 | 24.8 | 25.7 | ? |
| 10.0 | 31.0 | 31.8 | 30.9 | 32.1 | 31.2 | 31.4 | 31.4 |
Calculate the mean internode length for the plants treated with 5.0 mg dm-3 of gibberellin. Give your answer to one decimal place.
