Logan writes down his hypothesis that more salt will dissolve in cold water than in warm water.  He adds salt to different temperatures of water and records his observations including the amount of undissolved salt.  He finds that there is more salt dissolved in warm water than cold water.  What should Logan do next to make sure that his conclusion is valid?

A group of people trained to climb a mountain.  As they practice in high altitudes, Elise, a researcher, measured changes in their lung strength.  Why is it important that Elise's study has a control group?

Jace is studying states of matter by heating water in a pan.  Which statement from his notebook is an observation?

How many variables should be changed and tested in a simple experiment?