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The article "Chimps Aren't Charitable" (Newsday, November 2, 2005) summarized the results of a research study published in the journal Nature. In this study, chimpanzees learned to use an apparatus that dispensed food when either of two ropes was pulled. When one of the ropes was pulled, only the chimp controlling the apparatus received food. When the other rope was pulled, food was dispensed both to the chimp controlling the apparatus and also to a chimp in the adjoining cage. The accompanying data (approximated from a graph in the paper) represent the number of times out of 36 trials that each of seven chimps chose the option that would provide food to both chimps (the "charitable" response). 23 22 21 24 19 20 20 The figure below is a normal probability plot of these data. The plot is reasonably straight, so it seems plausible that the population distribution is approximately normal. Normal Score 19 20 21 22 23 24 Number of Charitable Respoases For purposes of this example, let's suppose it is reasonable to regard this sample of seven chimps as representative of the population of all chimpanzees. Calculation of a confidence interval for the population mean number of charitable responses requires x and o. From the given data, we compute x-21.29 S1.80