You are interested in determining which of two brands of batteries, brand a and brand b, lasts longer under differing conditions of use. one hundred fenix flashlights are fitted with brand a batteries and 100 olight flashlights are fitted with brand b batteries. each battery is used for 72 hours straight. the battery life is then measured for each battery, and the average battery life for the two brands is compared. what is wrong with this experimental design? not enough batteries of each type are used in the study. the experiment should have been conducted on more than two brands of flashlights. average battery life is not a proper measure for comparison. the type of flashlight is a confounding variable.