Question 508896
p = perimeter of the mat
p = 2(length + width)
p = 118
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l = 15 + 2x, where x is the width of the strip 
w = 20 + 2x
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2(15+2x+20+2x) = 118
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30 + 4x +40 + 4x = 118
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8x + 70 = 118
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8x = 48
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x = 6 in, which is the width of the border.
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Check to ensure the solution is the answer.
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l = 15 + 12 = 27
w = 20 + 12 = 32
32 + 27 = 59
p = 2*59 = 118
Correct.
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Answer: The width of the strip showing around the picture is 6 inches.
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Done.