Question

a 600 m long wire is used to fence a rectangular plot whose length is twice it's width.find the length and breadth of the plot

Answer 1

As you can see that a rectangular plot is a rectangle only, and 600 m long wire, the length of the wire used to fence the rectangular plot, is the perimeter. 

Let the width of the rectangle be x m. 
Length of the rectangle = 2x m

2(length+width) = perimeter
$2(2x+x) = 600$
$2(3x) = 600$
$6x = 600$
$\frac{6x}{6} = \frac{600}{6}$
$x = 100$
We have found the value of x. Now, we can find out the length and width of the plot. 
∴ Length of the plot = 2x m = (2 × 100) m = 200 m
   Width of the plot = x m = 100 m
I know that this question is from Algebra chapter. At first, I was also having doubt in this. 

Hope this may help you.