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Word Problems Involving Two Linear Equations in Two Variables
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B
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Number and Geometric Relations

Example 2

The length of a rectangular picture frame is 5 inches (in.) less than twice its width. Its perimeter is 32 in. What are its dimensions?



Solution

Represent the length and width of the picture frame (given in inches). Let x=length of the picture frame and y=width of the picture frame.

The length of the frame is 5 in. less than twice the width. Thus,

x=2y5.

The perimeter of the frame is 32 in. Applying the formula for the perimeter of a rectangle, you will get

2x+2y=32.

You now have a system of two linear equations in two variables.

{           x=2y5 2x+2y=32

To solve for y, substitute 2y5 for x in the second equation.

2(2y5)+2y =32
4y10+2y =32
6y =32+10
6y =42
y =7

To solve for x, substitute 7 for y in x=2y5.

x=2y5=2(7)5=145=9

Thus, the solution of the system is (9, 7).



Checking

The length of the frame (which is 9 in.) is 5 in. less than twice the width, which is 2(7)=14 in. The perimeter of the frame is

2(9)+2(7)=18+14=32 in.

The two numbers satisfy the conditions of the given problem. Thus, the length of the picture frame is 9 in. while its width is 7 in.