The concentration of carbon dioxide (CO2) in the atmosphere is increasing rapidly due to our use of fossil fuels. Because plants use CO2 to fuel photosynthesis, more CO2 may cause trees and other plants to grow faster. An elaborate apparatus allows researchers to pipe extra CO2 to a 30-meter circle of forest. They selected two nearby circles in each of three parts of a pine forest and randomly chose one of each pair to receive extra CO2. The response variable is the mean increase in base area for 30 to 40 trees in a circle during a growing season. We measure this in percent increase per year. Here are one year's data. Pair Control plot Treated plot
1 9.728 10.748
2 7.276 8.332
3 5.612 6.632

Required:
a. State the null and alternative hypotheses.
b. Explain clearly why the investigators used a one-sided alternative.

1. The researchers have no preconceived idea what extra CO2 will do to the growth rate.
2. The researchers have reason to believe that CO2 will decrease growth rate.
3. The researchers have reason to believe that CO2 will increase growth rate.

c. Carry out a test and report your conclusion in simple language.