Overview:  In this group, Carissa works to convince her group members that they should locate the new grocery store in Sycamore, where sales tax is slightly less than in the other towns.  Trey devises a solution of measuring approximately two miles (1-inch) each from points D and E, and he locates a new point where these two segments meet.  The point that Trey marks is slightly north of Sycamore.  Carissa convinces the group that they should move their point slightly south of the point Trey identified, so that shoppers can benefit from the lower sales tax.

Prior knowledge:  Students combine their prior knowledge of school mathematics with their knowledge of the context of the problem.  By narrowing their focus to two points, Trey is able to measure to identify a new point that is (approximately) equidistant to those two points.  Carissa uses an argument based on her knowledge of the community, and the different sales tax in the different towns, to convince the group that they should move their new point slightly south from where Trey located the point based on his mathematical solution.

Other points of interest:  In this explore, Carissa provides the main catalyst for considering the contextual information of the problem.  In contrast to other explores, in which all students become overwhelmed by the contextual information of the problem, in this story the students are able to combine their contextual knowledge with a geometric solution.  Carissa persistently argues for the merits of seeking out lower sales tax, and she convinces her group to account for this with their solution.  Mathematically, Trey says that he has measured two miles each from point D and E, and his two line segments meet at a point.  However it is not clear from this vignette whether Trey has measured the angles.  Although he seems to be treating this as an isosceles triangle, it does not seem that Trey has actually made an isosceles triangle.