The focal point of an agricultural research study was the relationship between when a crop is planted and the amount of crop harvested. If a crop is planted too early or too late farmers may fail to obtain optimal yield and hence not make a profit. An ideal date for planting is set by the researchers, and the farmers then record the number of days either before or after the designated date. In the following data set, D is the deviation (in days) from the ideal planting date, and Y is the yield ( in bushels per acre) of a wheat crop:

a. Plot the above data. Does a linear relation appear to exist between yield and ­deviation from the ideal planting date?
b. Plot yield versus absolute deviation from the ideal planting date. Does a linear ­relation seem more appropriate in this plot than the plot in part (a)?

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D -1110-98-764 Y 438 44.0 448 474 481 468 499469 464 53.5 D 1 Y 55.0 46.9 4450.2 410 42.8 365 38 322 333 3 68 13 5 18 19