An agricultural scientist is investigating the effect of different concentrations of a nitrogen-based fertilizer on the growth rate of wheat shoots over 10 days. The increase in height of the shoots is recorded for three separate trials at each concentration.
The table below shows the results of this investigation:
| Fertilizer Concentration (g L−1g\text{ L}^{-1}g L−1) | Height increase of shoots in 10 days (mm\text{mm}mm) | ||||
|---|---|---|---|---|---|
| Trial 1 | Trial 2 | Trial 3 | Mean | Range | |
| 1.5 | 22 | 19 | 25 | 22 | 19–25 |
| 3.0 | 53 | 49 | 54 | ......... | 49–54 |
Calculate the missing mean height increase at a concentration of 3.0 g L-1 to complete the table. Show your working.
Identify which variable (Fertilizer Concentration or Height increase) should be plotted on the x-axis.
Explain how knowing the range of the trials helps the investigator when drawing conclusions from a graph of these results.