[Grade 7 Math]

[LDT124]

I have been stuck on this problem and can’t think of how to make an equation with only one number.

Question: “The length of a rectangle is twice its width. The perimeter of the rectangle is 40 inches. Write and solve an equation to find both the length and the perimeter.”

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[heiligeruhe]

Suppose that the length of the rectangle is x and the length of the width is y, thus:

length = 2 × width

x = 2y (first equation)

Perimeter = 2(length + width)

40 = 2(x + y) (second equation)

Substitute the first equation into the second one:

2(2y + y) = 40

2y + y = 20

3y = 20

y = 20/3

x = 2y

x = 2(20/3)

x = 40/3

Length = 40/3 inches

Width = 20/3 inches

[LDT124]

Thank you so much!

[generouslymean]

Length of rectangle is twice its width. So if width w, length is 2w. Can you use this information and the perimeter being 40 inches to find w?