GRE Math : How to find the length of the side of a rectangle

Study concepts, example questions & explanations for GRE Math

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Example Questions

Example Question #1346 : Gre Quantitative Reasoning

A rectangle has an area of 48 and a perimeter of 28.  What are its dimensions?

Possible Answers:

6 x 8

0.25 x 192

1 x 48

16 x 3

2 x 24

Correct answer:

6 x 8


We can set up our data into the following two equations:

(Area) LH = 48

(Perimeter) 2L + 2H = 28

Solve the area equation for one of the two variables (here, length): L = 48 / H

Place that value for L into ever place you find L in the perimeter equation: 2(48 / H) + 2H = 28; then simplify:

96/H + 2H = 28

Multiply through by H: 96 + 2H2 = 28H

Get everything on the same side of the equals sign: 2H2 - 28H + 96 = 0

Divide out the common 2: H2 - 14H + 48 = 0

Factor: (H - 6) (H - 8) = 0

Either of these multiples can be 0, therefore, consider each one separately:

H - 6 = 0; H = 6

H - 8 = 0; H = 8

Because this is a rectangle, these two dimensions are the height and width.  If you choose 6 for the "height" the other perpendicular dimension would be 8 and vice-versa.  Therefore, the dimensions are 6 x 8.

Example Question #1347 : Gre Quantitative Reasoning

The length of a rectangle is three times its width, and the perimeter is . What is the width of the rectangle?

Possible Answers:

Correct answer:


For any rectangle, \dpi{100} \small P=2L+2W, where \dpi{100} \small P=perimeter, \dpi{100} \small L=length, and \dpi{100} \small W=width

In this problem, we are given that \dpi{100} \small L=3W (length is three times the width), so replace \dpi{100} \small L in the perimeter equation with \dpi{100} \small 3W: \dpi{100} \small P=2(3W)+2W

Plug in our value for the perimeter, \dpi{100} \small P:

\dpi{100} \small 16=2(3W)+2W


\dpi{100} \small 16=6W+2W 

\dpi{100} \small 16=8W

\dpi{100} \small W=2

Example Question #1348 : Gre Quantitative Reasoning

The area of a rectangle is . Its perimeter is . What is the length of its shorter side?

Possible Answers:

Correct answer:


We know that the following two equations hold for rectangles. For area:

For perimeter:

Now, for our data, we know:

Now, solve the first equation for one of the variables:

Now, substitute this value into the second equation:

Solve for :

Multiply both sides by :

Solve as a quadratic. Divide through by :

Now, get the equation into standard form:

Factor this:

This means that  (or ) would equal either  or . Therefore, your answer is .


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