ACT Math : Plane Geometry

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #1 : How To Find The Area Of A Square

Midpointsquare

Given square \(\displaystyle ABCD\), with midpoints on each side connected to form a new, smaller square.  How many times bigger is the area of the larger square than the smaller square?

Possible Answers:

\(\displaystyle 2\)

\frac{\sqrt{2}}{2}\(\displaystyle \frac{\sqrt{2}}{2}\)

\(\displaystyle 4\)

\sqrt{2}\(\displaystyle \sqrt{2}\)

2\sqrt{2}\(\displaystyle 2\sqrt{2}\)

Correct answer:

\(\displaystyle 2\)

Explanation:

Assume that the length of each midpoint is 1.  This means that the length of each side of the large square is 2, so the area of the larger square is 4 square units.A=s^{2}\(\displaystyle A=s^{2}\)

To find the area of the smaller square, first find the length of each side.  Because the length of each midpoint is 1, each side of the smaller square is \sqrt{2}\(\displaystyle \sqrt{2}\) (use either the Pythagorean Theorem or notice that these right trianges are isoceles right trianges, so s, s, s\sqrt{2}\(\displaystyle s, s, s\sqrt{2}\) can be used).  

The area then of the smaller square is 2 square units.

Comparing the area of the two squares, the larger square is 2 times larger than the smaller square.

Example Question #1 : Squares

If a completely fenced-in square-shaped yard requires 140 feet of fence, what is the area, in square feet, of the lot?

Possible Answers:

140

4900

35

70

1225

Correct answer:

1225

Explanation:

Since the yard is square in shape, we can divide the perimeter(140ft) by 4, giving us 35ft for each side. We then square 35 to give us the area, 1225 feet. 

Example Question #391 : Plane Geometry

The perimeter of a square is \(\displaystyle 50\) \(\displaystyle \textup{in}\). What is its area?

Possible Answers:

\(\displaystyle 175.25\) \(\displaystyle \textup{in}^2\)

\(\displaystyle 156.25\) \(\displaystyle \textup{in}^2\)

\(\displaystyle 125\) \(\displaystyle \textup{in}^2\)

\(\displaystyle 144\) \(\displaystyle \textup{in}^2\)

\(\displaystyle \textup{Not enough information provided}\)

Correct answer:

\(\displaystyle 156.25\) \(\displaystyle \textup{in}^2\)

Explanation:

The perimeter of a square is very easy to calculate. Since all of the sides are the same in length, it is merely:

\(\displaystyle 4s=p\)

\(\displaystyle 4s=50\)

\(\displaystyle s=12.5\)

From this, you can calculate the area merely by squaring the side's value:

\(\displaystyle A = 12.5^2=156.25\) \(\displaystyle \textup{in}^2\)

Example Question #2 : How To Find The Area Of A Square

What is the area of a square with a side length of \(\displaystyle 14\textup{yd}\)?

Possible Answers:

\(\displaystyle 196\) \(\displaystyle \textup{yd}^2\)

\(\displaystyle 86\) \(\displaystyle \textup{yd}^2\)

\(\displaystyle 56\) \(\displaystyle \textup{yd}^2\)

\(\displaystyle 144\) \(\displaystyle \textup{yd}^2\)

\(\displaystyle 96\) \(\displaystyle \textup{yd}^2\)

Correct answer:

\(\displaystyle 196\) \(\displaystyle \textup{yd}^2\)

Explanation:

The area of a square is very easy. You merely need to square the length of any given side. That is, the area is defined as:

\(\displaystyle A=s^2\)

For our data, this is:

\(\displaystyle A=14^2=196\)

Example Question #1 : How To Find The Area Of A Square

What is the area of a square with a perimeter of \(\displaystyle 48\) ft?

Possible Answers:

\(\displaystyle 48ft^2\)

Not enough information is given.

\(\displaystyle 144ft^2\)

\(\displaystyle 576ft^2\)

\(\displaystyle 144ft\)

Correct answer:

\(\displaystyle 144ft^2\)

Explanation:

For a square all the sides are equal, and there are four sides, so divide the perimeter by 4 to determine the side length. 

\(\displaystyle s = 48/4 = 12\).

Next to find the area of a square, square the side length: 

\(\displaystyle A = s^2 = 12^2 = 144ft^2\).

Don't forget your units!

Example Question #1 : How To Find The Area Of A Square

Eric has 160 feet of fence for a parking lot he manages. If he is using all of the fencing, what is the area of the lot assuming it is square?

Possible Answers:

\(\displaystyle 16,000\ feet^{2}\)

\(\displaystyle 1600\ feet^{2}\)

\(\displaystyle 160\ feet^{2}\)

\(\displaystyle 80\ feet^{2}\)

\(\displaystyle 1200\ feet^{2}\)

Correct answer:

\(\displaystyle 1600\ feet^{2}\)

Explanation:

The area of a square is equal to its length times its width, so we need to figure out how long each side of the parking lot is. Since a square has four sides we calculate each side by dividing its perimeter by four.

\(\displaystyle \frac{160}{4}=40\)

Each side of the square lot will use 40 feet of fence.

\(\displaystyle Area=length \times width\)

\(\displaystyle 40\ ft\times 40\ ft=1600\ ft^{2}\).

Example Question #6 : How To Find The Area Of A Square

A square garden is inscribed inside a circular cobblestone path. If the radius of the cobblestone path is \(\displaystyle 45\) feet, what is the area of the garden?

Possible Answers:

\(\displaystyle 2500ft^2\)

\(\displaystyle 5000ft^2\)

\(\displaystyle 4050ft^2\)

\(\displaystyle 3850ft^2\)

\(\displaystyle 2700ft^2\)

Correct answer:

\(\displaystyle 4050ft^2\)

Explanation:

If a square is inscribed inside a circle, the diameter of the circle is the diagonal of the square. Since we know the radius of the circle is \(\displaystyle 45\) feet, the diameter must be \(\displaystyle 90\) feet. Thus, the diagonal of the square garden is \(\displaystyle 90\) feet.

All squares have congruent sides; thus, the diagonal of a square creates two isosceles right triangles. The ratio of the lengths of the sides of an isosceles right triangle are \(\displaystyle x: x: x\sqrt2\), where \(\displaystyle x\sqrt2\) is the hypotenuse. Thus, to find the length of a side of a square from the diagonal, we must divide by \(\displaystyle \sqrt2\).

\(\displaystyle s = \frac{90}{\sqrt2} = \frac{90\sqrt2}{2} = 45\sqrt2\)

The area of a square is \(\displaystyle A = s^2\), so if one side is \(\displaystyle 45\sqrt2\), our area is

\(\displaystyle A = s^2 = (45\sqrt2)^2 = (2025\cdot 2) = 4050\)

Thus, the area of our square garden is \(\displaystyle 4050ft^2\)

Example Question #2 : How To Find The Area Of A Square

Find the area of a square whose side length is \(\displaystyle 1\).

Possible Answers:

\(\displaystyle 4\)

\(\displaystyle 2\)

\(\displaystyle 1\)

\(\displaystyle 10\)

Correct answer:

\(\displaystyle 1\)

Explanation:

To find area, simply square the side length. Thus,

\(\displaystyle A=1^2=1\)

Example Question #11 : Squares

Find the area of a square with side length 5.

Possible Answers:

\(\displaystyle 20\)

\(\displaystyle 10\)

\(\displaystyle 5\)

\(\displaystyle 25\)

Correct answer:

\(\displaystyle 25\)

Explanation:

To solve, simply use the formula for the area of a square given side length s. Thus,

\(\displaystyle A=s^2=5^2=25\)

Example Question #431 : Quadrilaterals

Square

A square is circumscribed on a circle with a 6 inch radius. What is the area of the square, in square inches?

Possible Answers:

144

24

48

\(\displaystyle 36\pi\)

36

Correct answer:

144

Explanation:

We know that the radius of the circle is also half the length of the side of the square; therefore, we also know that the length of each side of the square is 12 inches.

Square

We need to square this number to find the area of the square.

\(\displaystyle A=s^2\)

\(\displaystyle A=12^2\)

\(\displaystyle A=144\)

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