This paper demonstrates the practical application of two-variable linear inequalities through a shipping logistics problem. Beginning with a graph showing truck capacity constraints for televisions and refrigerators, the paper derives a linear inequality equation using point-slope form. The analysis includes testing specific shipment combinations against the inequality, determining maximum shipment quantities under new constraints, and visualizing solution regions graphically. The paper illustrates how inequalities model real-world constraints and how substitution methods can optimize resource allocation within those constraints.
Two-variable inequalities consist of an independent variable and a dependent variable. This paper examines a practical application of two-variable inequalities through a shipping logistics problem. Graphic representations illustrate the range of possible solutions that satisfy the given constraints.
The problem is based on a shipping truck that can carry a maximum of 330 televisions and no refrigerators, or a maximum of 110 refrigerators and no televisions. The graph representing this constraint shows refrigerators on the x-axis and televisions on the y-axis. The graph features a solid line rather than a dashed line, which indicates that the points on the line itself are part of the solution set. The two key points on the line are (0, 330) and (110, 0).
Using these points, the slope of the line can be calculated. The slope formula is (y₁ − y₂)/(x₁ − x₂). Substituting the coordinates:
(330 − 0)/(0 − 110) = 330/(−110) = −3
The slope of the line is −3. Using point-slope form, the equation can be derived as follows:
y − y₁ = m(x − x₁) (point-slope form)
y − 330 = −3(x − 0) (substitute slope and point)
y = −3x + 330 (apply distributive property and simplify)
3x + y ≤ 330 (add 3x to both sides and change to less-than-or-equal-to symbol)
The resulting two-variable linear inequality is 3x + y ≤ 330, which models the truck's capacity constraint.
To verify whether specific shipment quantities are feasible, test points can be substituted into the inequality. The first scenario asks whether the truck can hold 71 refrigerators and 118 televisions. The point (71, 118) must be tested against the inequality:
3x + y ≤ 330 (original inequality)
3(71) + 1(118) ≤ 330 (substitute x = 71, y = 118)
213 + 118 ≤ 330 (multiply and add)
331 ≤ 330 (evaluate)
This statement is false. Therefore, the truck cannot hold this combination because 331 exceeds the capacity of 330.
The second scenario asks whether the truck can hold 51 refrigerators and 176 televisions. Testing the point (51, 176):
3x + y ≤ 330 (original inequality)
3(51) + 1(176) ≤ 330 (substitute x = 51, y = 176)
153 + 176 ≤ 330 (multiply and add)
329 ≤ 330 (evaluate)
"Optimize shipment amounts given new limits"
If 200 televisions are shipped, the maximum number of refrigerators that can be shipped is 43. The solution region would be a triangular area bounded by the constraint line, the vertical axis, and the horizontal line at y = 200, containing all feasible shipment combinations.
This analysis demonstrates how two-variable inequalities model real-world constraints and provide a systematic method for decision-making. An inequality was derived from graphical data by identifying key points and applying point-slope form. The solid boundary line indicated that points on the line itself satisfied the inequality. Test points were then used to verify whether specific shipments could be made. Finally, substitution of one variable allowed optimization of the other variable to determine maximum allowable quantities under different scenarios. Whether determining feasibility of proposed shipments or optimizing quantities under new constraints, the inequality serves as a powerful tool for logistics planning and resource allocation.
Dugopolski, M. (2012). Elementary and Intermediate Algebra (4th ed.). McGraw-Hill Publishing.
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