In order to increase the production of gas wells, a procedure known as "fracture treatment" is often used. Fracture fluid, which consists of fluid mixed with sand, is pumped into the well. The following figure presents a scatterplot of the monthly production versus the volume of fracture fluid pumped for 255 gas wells. Both production and fluid are expressed in units of volume per foot of depth of the well. The least-squares line is superimposed. The equation of the least-squares line is y = 106.11 + 0.1119x.

a. From the least-squares line, estimate the production for a well into which 4000 gal/ft are pumped.
b. From the least-squares line, estimate the production for a well into which 500 gal/ft are pumped.
c. A new well is dug, and 500 gal/ft of fracture fluid are pumped in. Based on the scatterplot, is it more likely that the production of this well will fall above or below the least-squares estimate?
d. What feature of the scatterplot indicates that assumption 3 on page 540 is violated?

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1600 1400 1200 1000 ︶ 600F.. 400 200 0 0 2000 4000 6000 8000 Fracture fluid (gal/ft)