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Length is twice it's width - what's its length?

A rectangular yard is enclosed with 840 metres of fencing material; that is, its perimeter is 840m. Its length is twice its width.
What is its length in metres?

So this is my working, P=840 and W=2L

P=4L+2W
840=4L+2(2L)
840=4L+4L
840=8L
L=15m

This is wrong, the answer is 280m but I don't know how to find it.
Original post by Airess3
A rectangular yard is enclosed with 840 metres of fencing material; that is, its perimeter is 840m. Its length is twice its width.
What is its length in metres?

So this is my working, P=840 and W=2L

P=4L+2W
840=4L+2(2L)
840=4L+4L
840=8L
L=15m

This is wrong, the answer is 280m but I don't know how to find it.


If the width of one side is W then the length of one side is 2W, so when working out the perimeter you would have:
P=2L+2W
=2(2W)+2W

Solving the above you would get the width of the rectangle which you can double to find the length.


Posted from TSR Mobile
(edited 8 years ago)
Original post by MathQ123
If the width of one side is W then the length of one side is 2W, so when working out the perimeter you would have:
P=2L+2W
=2(2W)+2W

Solving the above you would get the width of the rectangle which you can double to find the length.


Posted from TSR Mobile


Thanks!

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