How many corn plants are too many? How much corn per acre should a farmer plant to obtain the highest yield? To find the best planting rate, do an experiment: plant at different rates on several plots of ground and measure the harvest. Here are data from such an experiment:

Plants per acre Yield (bushels per acre)

12,000 150.1 113.0 118.4 142.6 16,000 166.9 120.7 135.2 149.8 20,000 165.3 130.1 139.6 149.9 24,000 134.7 138.4 156.1 28,000 119.0 150.5

(a) Is yield or planting rate the explanatory variable? Why?

(b) Make a scatterplot of yield and planting rate.

(c) Describe the overall pattern of the relationship. Is it a straight line? Is there a positive or negative association, or neither? Explain why increasing the number of plants per acre of ground has the effect that your graph shows.