ISEE Upper Level Math : How to find the area of a square

Example Questions

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

A square is made into a rectangle by increasing the width by 20% and decreasing the length by 20%.  By what percentage has the area of the square changed?

the area remains the same

decreased by 10%

decreased by 4%

increased by 20%

decreased by 4%

Explanation:

The area decreases by 20% of 20%, which is 4%.

The easiest way to see this is to plug in numbers for the sides of the square.  If we are using percentages, it is easiest to use factors of 10 or 100.  In this case we will say that the square has a side length of 10.

10% of 10 is 1, so 20% is 2.  Now we can just increase one of the sides by 2, and decrease another side by 2.  So our rectangle has dimensions of 12 x 8 instead of 10 x 10.

The original square had an area of 100, and the new rectangle has an area of 96. So the rectangle is 4 square units smaller, which is 4% smaller than the original square.

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

Side  shown in the diagram of square  below is equal to 21cm. What is the area of ?

Cannot be determined

Explanation:

To find the area of a quadrilateral, multiply length times width. In a square, since all sides are equal,  is both the length and width.

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

If Amy is carpeting her living room, which meaures feet by feet, how many square feet of carpet will she need?

Explanation:

To find the area of the floor, multiply the length of the room by the width (which is the same forumla used to find the area of a square).  The equation can be written:

Substitute feet for and feet for :

Amy will need of carpet.

Example Question #4 : How To Find The Area Of A Square

A rectangle and a square have the same perimeter. The rectangle has length  centimeters and width  centimeters. Give the area of the square.

Explanation:

The perimeter of the rectangle is

centimeters.

This is also the perimeter of the square, so divide this by  to get its sidelength:

centimeters.

The area is the square of this, or  square centimeters.

Example Question #11 : Squares

Four squares have sidelengths 4 inches, 8 inches, 12 inches, and 16 inches. What is the average of their areas?

Explanation:

The areas of the four squares can be calculated by squaring their sidelengths. Add these areas, then divide by 4:

square inches

Example Question #12 : Squares

Which of the following is equal to the area of a square with sidelength  yards?

Explanation:

Multiply the sidelength by 36 to convert from yards to inches:

Square this to get the area:

square inches

Example Question #4 : How To Find The Area Of A Square

What is the area of a square in which the length of one side is equal to ?

Explanation:

The area of a square is equal to the product of one side multiplied by another side. Therefore, the area will be equal to:

The next step is to convert the fractions being added together to a form in which they have a common denominator. This gives us:

Example Question #8 : How To Find The Area Of A Square

One of the sides of a square on the coordinate plane has its endpoints at the points with coordinates  and . What is the area of this square?

Explanation:

The length of a segment with endpoints  and  can be found using the distance formula with :

This is the length of one side of the square, so the area is the square of this, or 122.

Example Question #9 : How To Find The Area Of A Square

One of the sides of a square on the coordinate plane has its endpoint at the points with coordinates  and , where  and  are both positive. Give the area of the square in terms of  and .

Explanation:

The length of a segment with endpoints  and  can be found using the distance formula as follows:

This is the length of one side of the square, so the area is the square of this, or .

Example Question #10 : How To Find The Area Of A Square

One of the vertices of a square is at the origin. The square has area 13. Which of the following could be the vertex of the square opposite that at the origin?

Explanation:

Since a square is a rhombus, one way to calculate the area of a square is to take half the square of the length of a diagonal. If we let  be the length of each diagonal, then

Therefore, we want to choose the point that is  units from the origin. Using the distance formula, we see that  is such a point:

Of the other points:

:

:

:

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