Afootball coach gives half his players a protein bar to eat before each game; the other players do not receive the protein bar. after a month of games, he analyzes their playing stats. he concludes the protein bar improve their performance on the field. how can the coach test the means to be sure the results are not likely to happen by chance?

To make the sure the results did not happen by chance, the coach can ensure that the protein bars are the only difference between the two groups. For example, he can make sure that both groups are drinking the same amounts of water and getting in the same amount of practice; that way, he will be able to determine that one group is performing better due to the protein bars only. Also, the coach can repeat this experiment multiple times to make sure that the results weren't a random, one-time thing. 

Subtracting is the opposite of adding

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