Question 830863
We know that the perimeter (like a fence) is 2 pieces of the length and 2 pieces of the width.  P = 2L + 2W
The problem tells us that L = 3W ("length is three times its width")
The perimeter is given as 100'.
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Now we just have to plug in the values.
100 (P) = 2L + 2W
Substitute the value for L
100 = 2(3W) + 2W
Multiply
100 = 6W + 2W
Add
100 = 8W
Divide each side by 8
12.5 = W
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Now that we know W, we can find L ("length is three times its width")
L = 3* W (12.5)
L = 37.5
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Let's check to be certain.
P = 2(37.5) + 2(12.5)
P = 75 + 25
100 = 75 + 25
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Success!