Question: A neuroscientist measures the reaction times (in seconds) during an experimental session in a sample of cocaine-addicted (n = 8), morphine-addicted (n = 12), and heroin-addicted rats (n = 6). Mean reaction times in each sample are 11, 18, and 13 seconds, respectively. What is the weighted mean for all three samples? Hint: The overall mean is not 14.0 seconds.