ACT Math : Plane Geometry

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #3 : How To Find The Length Of The Diagonal Of A Quadrilateral

Q12

In the parallelogram above,  and . What is the length of the diagonal ?

Possible Answers:

Correct answer:

Explanation:

In a parallelogram, the two diagonals bisect each other at their centers. Therefore, . To find , we set them equal to one another and solve. 

Plugging this value back into both equations, then adding those values together, gives us our answer of

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

Jane plans to re-tile her kitchen with tiles that have a length of  inches and a width of  inches wide. If her kitchen measures  feet by  feet, how many tiles will she need?

Possible Answers:

Correct answer:

Explanation:

When attempting to solve how many pieces of a particular object you need to cover a certain area, always make sure that your units of measurement (for the object and for the area you are covering) are the same. In the case of this question, the units of measurement are different, so you must first convert all measurements to use the same unit.

 

Since the tiles being used to cover the area are measured in inches, convert all units given to inches:

Length:  feet   inches

Width:  feet   inches

Then, find the area of the entire space you are covering. Since the space is rectangular (this can be assumed since only length and width are given as measurements), multiply the length and width to find the total area:  square inches.

 

Next, find the area of each of the tiles:  square inches. Divide the total area of the space by the area of each of your tiles: . In cases where you are covering a certain area with an object, always round up if you have a decimal (no matter how small), because you cannot simply buy  of a tile.

 

The answer is .

Example Question #421 : Geometry

Vikram is looking at a scale drawing of a room he is building. The drawing is of a rectangle that measures  inches by  inches. If he knows the length of the longer side of the room will measure  feet, what is the area of the room?

Possible Answers:

Correct answer:

Explanation:

When solving such problems, always make sure that your units of measurement are all the same. In the case of this problem, you must convert feet to inches. Multiply 30 by 12 in order to get its equivalent in inches.

We know that the 30 feet corresponds with the side of the drawing that is 18 inches because it is stated that the longest side will be 30 feet. Divide 360 by 18 in order to find the ratio of the actual size of the room to the measurements on the drawing

This means that the actual measurements of the room are 20 times the measurements of the drawing. Multiply 20 times 12 in order to find the measurement of the shorter side in inches.

Divide both the 360 and 240 by 12 to convert the measurements back into feet.

Then multiply the results to get the final answer.

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

If a trapezoid has base lengths of  and  and a height of , what is its area?

Possible Answers:

Correct answer:

Explanation:

Use the formula for area of a trapezoid:

Where  is the area,  and  are the lengths of the two bases, and  is the height.

In this case:

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

A parallelogram has a side length of , a height of , and a base length of . What is its area?

Possible Answers:

Correct answer:

Explanation:

Use the formula for area of a parallelogram:

Where  is the area,  is the base length, and  is the height.

In this case:

Example Question #1 : How To Find The Length Of The Side Of A Quadrilateral

Find the length of a rectangle if the area is , and the width is .

Possible Answers:

Correct answer:

Explanation:

Write the formula to solve the area of a rectangle.

Substitute the dimension and area to solve for the length.

Example Question #1 : How To Find The Length Of The Side Of A Quadrilateral

If the perimeter of a square is  and the area is , what is the side length of the square?

Possible Answers:

Correct answer:

Explanation:

The square has 4 equal sides.  Let's assume a side is .

Each side of the square has a length of .

The area of the square is:

Substitute  into the area to solve for .

Since one side of the square is , substitute the value of   to determine the length of the square side.

Example Question #1 : How To Find The Length Of The Side Of A Quadrilateral

Find the side of a square if the area is .

Possible Answers:

Correct answer:

Explanation:

The area of a square is:

Substitute the area and solve for the side.

The quantity inside the square root may not be factorized in attempt to eliminate the square root!

The side length of the square is:

Example Question #4 : How To Find The Length Of The Side Of A Quadrilateral

Q9

Find the perimeter of the rhombus above. 

Possible Answers:

Correct answer:

Explanation:

By definition, a rhombus is a quadrilateral with four equal sides whose angles do not all equal 90 degrees. To find the perimeter, we must find the values of x and y. In order to do so, we must set up a system of equations where we set two sides equal to each other. Any two sides can be used to create these systems.

Here is one example:

Eq. 1

Eq. 2

 

Now we plug  into the first equation to find the value of :

Plugging these values into any of the three equations will give us the length of one side equaling 11.

Since there are four sides, .

Example Question #1 : How To Find An Angle In A Quadrilateral

Q6

 bisects . If  then, in degrees, what is the value of ?

Possible Answers:

Correct answer:

Explanation:

A rectangle has two sets of parallel sides with all angles equaling 90 degrees. 

Since  bisects  into two equal parts, this creates an isosceles triangle .

Therefore . The sum of the angles in a triangle is 180 degrees.

Therefore 

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