Original Project
Control of Variables
If more than one variable changes at the same time in an experiment, the outcome of the experiment may not be cl…
Item CR021003: In an experiment on the effect of temperature and soil type on the growth of corn plants, with both variables changing at the same time, no conclusion can be reached regarding the effect of either temperature or soil type on the growth of the plants.
A farmer wants to find out which type of soil is best for growing his corn. He also wants to find out which type of fertilizer is best for growing his corn.
He does the following experiment using two different types of soil and two different types of fertilizer:
What can the farmer conclude from this experiment?
- He can conclude that Soil B is the best soil for growing his corn.
- He can conclude that Fertilizer Y is the best fertilizer for growing his corn.
- He can conclude that Soil B is the best soil for growing his corn and that Fertilizer Y is the best fertilizer for growing his corn.
- It is NOT possible to conclude from this experiment which soil is best for growing his corn or which fertilizer is best for growing his corn.
- Distribution of Responses
- Students Responding Correctly
| Group | Correct | Total | Percent |
|---|---|---|---|
| Overall | 676 | 2498 | 27% |
| Grades | |||
| 6–8 | 260 | 1419 | 18% |
| 9–12 | 413 | 1070 | 39% |
| Gender | |||
| Male | 337 | 1227 | 27% |
| Female | 325 | 1232 | 26% |
| Primary Language | |||
| English | 600 | 2143 | 28% |
| Other | 58 | 291 | 20% |