What is the most difficult part of a controlled experiment?

Testing multiple variables is the most difficult part of a controlled experiment.

Explanation:

An experiment in which one or some of the factors are varying with respect to time and while the other factors are maintained constant is known as a controlled experiment. More the number of testable variables more will be the issue in obtaining a conclusion, at the same time what would be the factors that should be kept constant will also become a problem. Thus, using multiple variables for examining can become tough in a controlled experiment.

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what do the different brain waves do?

explanation:

brainwaves are produced by synchronised electrical pulses from masses of neurons communicating with each other. brainwaves are detected using sensors placed on the scalp. brainwave speed is measured in hertz (cycles per second) and they are divided into bands delineating slow, moderate, and fast waves.

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