400
Ms. Monroe observed that her Sprite lost its carbonation when it sat on her desk during the day. She wanted to investigate how long it would take to lose its carbonation so she set out a Coke in the morning, a Sprite in the afternoon, a Diet Coke in the evening and checked back the next day to see if they were flat. Is this a fair test? Explain why.
No it is not, because she changed two variables - the soda and the amount of time.