How to make geometric comparisons - HSPT Quantitative

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Question

Examine (a), (b), and (c) and find the best answer.

a) The area of a square with a side length of

b) The area of a square with a side length of

c) The area of a circle with a radius of

Answer

a) The area of a square with a side length of

To find the area of a square, square the side length:

b) The area of a square with a side length of

c) The area of a circle with a radius of

To find the area of a circle, multiply the radius by .

(Here, we rounded to , because an exact number isn't necessary to answer the question.)

Therefore (c) is larger than (b) which is larger than (a).

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Question

Examine (a), (b), and (c) to find the best answer:

a) area of a circle with a diameter of

b) area of a circle with a radius of

c) area of a circle with a cirucumference of

Answer

All of these circles have the same diameter, so they all must have the same area:

a) area of a circle with a diameter of

b) area of a circle with a radius of

c) area of a circle with a cirucumference of

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Question

Examine (a), (b), and (c) to find the best answer:

a) area of a rectangle with side lengths and

b) area of a rectangle with side lengths and

c) area of a square with side length

Answer

Area is calculated by multiplying the side lengths:

a) area of a rectangle with side lengths and

b) area of a rectangle with side lengths and

c) area of a square with side length

Therefore (b) is less than (a), which is less than (c).

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Question

Examine (a), (b), and (c) to find the best answer:

a) perimeter of a square with a side length of

b) perimeter of a rectangle with a length of and a width of

c) perimeter of an equailateral triangle with a side length of

Answer

To find perimeter, add up the lengths of all the sides:

a)

b)

c)

(a) and (b) are equal, and they are smaller than (c)

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Question

Examine (a), (b), and (c) to find the best answer:

a) perimeter of a square with a side length of

b) circumference of a circle with a diameter of

c) perimeter of an equilateral triangle with a side length of

Answer

Find perimeter by adding up the lengths of the sides of the shape. Find circumference by multiplying the diameter by :

a) perimeter of a square with a side length of

b) circumference of a circle with a diameter of

c) perimeter of an equilateral triangle with a side length of

Therefore (a) and (c) are equal, and they are greater than (b).

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Question

Examine (a), (b), and (c) to find the best answer:

a) circumference of a circle with a radius of

b) circumference of a circle with a diameter of

c) diameter of circle with a circumference of

Answer

The formulas to remember for this problem are (Circumference equals diameter times pi) and (diameter equals two pi).

a) circumference of a circle with a radius of

b) circumference of a circle with a diameter of

c) diameter of circle with a circumference of

Therefore (a) is the greatest, followed by (b), then (c).

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Question

Examine (a), (b), and (c) to find the best answer:

a) area of a square with a perimeter of

b) area of a square with a side length of

c) area of a square with a side length of

Answer

Things to remember here are that area is found by squaring side length and that side length is of the perimeter.

a)

b)

c)

(c) is the greatest, and none of the values are equal.

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Question

Examine (a), (b), and (c) to find the best answer:

a) the sum of the interior angles of a triangle

b) the sum of the interior angles of a square

c) the total degrees in a circle

Answer

The sum of the interior angles of a triangle is always degrees. For squares, it's always degrees. There are also a total of degrees in a circle. Therefore, (b) and (c) are equal, and they are greater than (a).

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Question

Examine (a), (b), and (c) to find the best answer:

a) area of a square with side length

b) area of a square with perimeter

c) area of a square with side length

Answer

The area of a square is the side length squared. The perimeter is the side length multiplied by .

(b) and (c) are equal because a side length should be of the perimeter. (a) is the greatest, because the greatest side length leads to the greatest area.

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Question

Examine (a), (b), and (c) to find the best answer:

a) a circle with a radius of

b) a circle with a diameter of

c) a circle with a circumference of

Answer

The circle with the greatest radius is also going to have the greatest area, because .

Use these formulas to find the radius of each circle:

and , so in (b), .

and , so in (c), .

Compare these to (a), with .

Therefore (c) has the largest radius, so it also has the largest area.

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Question

Examine (a), (b), and (c) to find the best answer

a) a square with an area of

b) a square with a side length of

c) a square with a perimeter of

Answer

All of these squares are equal! We can tell because they all have the same side length. For (a), find the square root of the area to find the side length:

For (c), divide the perimeter by four to find the side length:

For (b), we are told that the side length equals .

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Question

Examine (a), (b), and (c) to find the best answer:

a) a circle with a circumference of

b) a circle with a radius of

c) a circle with a radius of

Answer

Circumference is found by multiplying the diameter by pi, so the diameter of (a) must be . Radius is half of diameter, so the radius of (a) must be . This means that (a) is equal to (c), but not (b).

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Question

Examine (a), (b), and (c) to find the best answer:

a) a circle with a radius of

b) a circle with a radius of

c) a circle with an area of

Answer

Find the radius of (c) to compare it to (a) and (b).

Since area is , we know that must be and that the square root of must be .

Since the radius of (c) is equal to the radius of (b), the circles are equivalent.

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Question

Examine (a), (b), and (c) to find the best answer:

a) side length of a cube with a volume of inches cubed

b) side length of a square with an area of inches squared

c) side length of a square with an area of inches squared

Answer

To find the side length of a cube from its volume, find the cube root:

To find the side length of a square from its area, find the square root:

b)

c)

(a) is smaller than (c), which is smaller than (b)

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Question

Examine (a), (b), and (c) to find the best answer:

a) the diameter of a circle

b) twice the radius of a circle

c) the circumference of a circle divided by

Answer

Diameter is found using this formula, which shows that it is twice the radius:

Circumference is found using this formula:

Manipulate this to find that diameter is also circumference divided by :

Therefore, all of these expressions are the same.

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Question

Examine (a), (b), and (c) to find the best answer:

a) perimeter of a square with an area of

b) perimeter of a square with an area of

c) perimeter of a square with a side length of

Answer

If you have the area of a square, you can find the side length by finding the square root. Then multiply by four to find the perimeter:

a)

b)

If you are given the side length, simply multiply by :

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Question

Examine (a), (b), and (c) to find the best answer:

(a) area of an equilateral triangle

(b) area of an isoceles triangle

(c) area of a right triangle

Answer

The shape of a triangle does not affect its size. Without knowing any dimensions, we cannot determine how large any of the areas are.

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Question

Circle has a radius of inches, a circumference of inches, and an area of inches squared.

Now imagine three other circles:

a) Circle has a radius of

b) Circle has a circumference of

c) Circle has an area of

Answer

Radius and circumference are related to each other by a direct proportion (). This means that if you cut one in half, you cut the other in half. For this reason, circles and are both related to by the same proportion and are thus equivalent.

Area is related to radius exponentially (). Cutting the area in half does not cut the radius in half. Circle therefore cannot be equivalent to .

To test this out, try substituting some numbers in for , , and .

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Question

Examine (a), (b), and (c) to find the best answer:

a) volume of a cube with side length of inches

b) area of a square with a perimeter of inches

c) perimeter of a square with a side length of inches

Answer

Voume would be measured in inches cubed, area in inches squared, and perimeter in inches. These are different types of measurements and cannot be compared.

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Question

Examine (a), (b), and (c) to find the best answer:

a) area of a circle with a circumference of

b) area of a circle with a radius of

c) area of a circle with a diameter of

Answer

The diameter of a circle is twice its radius. Since the diameter in (c) is twice the radius in (b), these two are equal.

The circumference is the diameter multiplied by . Since the circumfrence in (a) is the diameter in (c) multiplied by , this is also equal.

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