SAT II Math I : 2-Dimensional Geometry

Study concepts, example questions & explanations for SAT II Math I

varsity tutors app store varsity tutors android store

Example Questions

Example Question #1 : Geometry

Swimming_pool

The above figure depicts the rectangular swimming pool at an apartment. The apartment manager needs to purchase a tarp that will cover this pool completely. However, because of the cutting device the pool store uses, the length and the width of the tarp must each be a multiple of three yards. Also, the tarp must be at least one yard longer and one yard wider than the pool.

What will be the minimum area of the tarp the manager purchases?

Possible Answers:

\(\displaystyle 198\textrm{ yd}^{2}\)

\(\displaystyle 315 \textrm{ yd}^{2}\)

\(\displaystyle 270 \textrm{ yd}^{2}\)

\(\displaystyle 216 \textrm{ yd}^{2}\)

\(\displaystyle 252 \textrm{ yd}^{2}\)

Correct answer:

\(\displaystyle 270 \textrm{ yd}^{2}\)

Explanation:

Three feet make a yard, so the length and width of the pool are \(\displaystyle \frac{50}{3} = 16 \frac{2}{3}\) yards and \(\displaystyle \frac{35}{3} = 11 \frac{2}{3}\) yards, respectively. Since the dimensions of the tarp must exceed those of the pool by at least one yard, the tarp must be at least \(\displaystyle 17 \frac{2}{3}\) yards by \(\displaystyle 12 \frac{2}{3}\) yards; but since both dimensions must be multiples of three yards, we take the next multiple of three for each.

The tarp must be 18 yards by 15 yards, so the area of the tarp is the product of these dimensions, or

\(\displaystyle 18 \times 15 = 270\) square yards.

Example Question #1 : Geometry

Triangle

Note: Figure NOT drawn to scale.

Refer to the figure above, which shows a square inscribed inside a large triangle. What percent of the entire triangle has been shaded blue?

Possible Answers:

Insufficient information is given to answer the question.

\(\displaystyle 44\frac{4}{9} \%\)

\(\displaystyle 25 \%\)

\(\displaystyle 33 \frac{1}{3} \%\)

\(\displaystyle 50 \%\)

Correct answer:

\(\displaystyle 44\frac{4}{9} \%\)

Explanation:

The shaded portion of the entire triangle is similar to the entire large triangle by the Angle-Angle postulate, so sides are in proportion. The short leg of the blue triangle has length 20; that of the large triangle, 30. Therefore, the similarity ratio is \(\displaystyle 3:2\). The ratio of the areas is the square of this, or \(\displaystyle 3^{2}:2^{2}\), or \(\displaystyle 9:4\)

The blue triangle is therefore \(\displaystyle \frac{4}{9}\) of the entire triangle, or \(\displaystyle \frac{4}{9} \times 100 = 44 \frac{4}{9} \%\) of it.

Example Question #3 : Geometry

Right_triangle

Note: Figure NOT drawn to scale.

Refer to the above diagram. What is the area of \(\displaystyle \Delta ABC\)?

Possible Answers:

\(\displaystyle 180\)

\(\displaystyle 144\)

\(\displaystyle 225\)

\(\displaystyle 210\)

Insufficient information is given to answer the problem.

Correct answer:

\(\displaystyle 180\)

Explanation:

If we see hypotenuse \(\displaystyle \overline{AC}\) as the base of the large triangle, then we can look at the segment perpendicular to it, \(\displaystyle \overline{BD}\), as its altitude. Therefore, the area of \(\displaystyle \Delta ABC\) is

\(\displaystyle A = \frac{1}{2} (AC) (BD)\)

\(\displaystyle AC = AD + DC = 6 + 24 = 30\).

\(\displaystyle BD\), as the length of the altitude corresponding to the hypotenuse, is the geometric mean of the lengths of the parts of the hypotenuse it forms; that is, the square root of the product of the two:

\(\displaystyle BD =\sqrt{ \left ( AD\right ) \left ( DC\right )} = \sqrt{6 \cdot 24} = \sqrt{144} = 12\)

The area of \(\displaystyle \Delta ABC\) is therefore

\(\displaystyle A = \frac{1}{2} (AC) (BD) = \frac{1}{2} \cdot 30 \cdot 12 = 180\)

Example Question #1 : Geometry

Swimming_pool

The above figure depicts the rectangular swimming pool at an apartment. The apartment manager needs to purchase a tarp that will cover this pool completely, but the store will only sell the material in multiples of ten square yards. How many square yards will the manager need to buy?

Possible Answers:

\(\displaystyle 180\textrm{ yd}^{2}\)

\(\displaystyle 160\textrm{ yd}^{2}\)

\(\displaystyle 190\textrm{ yd}^{2}\)

\(\displaystyle 200 \textrm{ yd}^{2}\)

\(\displaystyle 170\textrm{ yd}^{2}\)

Correct answer:

\(\displaystyle 200 \textrm{ yd}^{2}\)

Explanation:

Three feet make a yard, so the length and width of the pool are \(\displaystyle \frac{50}{3}\) yards and \(\displaystyle \frac{35}{3}\) yards; the area of the pool, and that of the tarp needed to cover it, must be the product of these dimensions, or

\(\displaystyle \frac{50}{3} \times \frac{35}{3}= \frac{1,750}{9} = 194 \frac{4}{9}\) square yards. 

The manager will need to buy a number of square yards of tarp equal to the next highest multiple of ten, which is 200 square yards.

Example Question #1 : Area

Right_triangle

Note: Figure NOT drawn to scale.

Refer to the above diagram. In terms of area, \(\displaystyle \Delta ADB\) is what fraction of \(\displaystyle \Delta ABC\)?

Possible Answers:

\(\displaystyle \frac{1}{6}\)

\(\displaystyle \frac{1}{4}\)

\(\displaystyle \frac{1}{3}\)

\(\displaystyle \frac{1}{5}\)

Insufficient information is given to answer this question.

Correct answer:

\(\displaystyle \frac{1}{5}\)

Explanation:

The area of \(\displaystyle \Delta ADB\), being right, is half the products of its legs, which is:

\(\displaystyle \frac{1}{2} (AD) (BD) = \frac{1}{2} \times 6 (BD) = 3 (BD)\)

 

The area of \(\displaystyle \Delta ABC\) is one half the product of its base and height; we can use its hypotenuse \(\displaystyle AC = AD + DC = 6 + 24 = 30\) as the base and \(\displaystyle BD\) as the height, so this area is

\(\displaystyle \frac{1}{2} (AC) (BD) = \frac{1}{2} \times 30 (BD) = 15 (BD)\)

 

Therefore, in terms of area, \(\displaystyle \Delta ADB\) is \(\displaystyle \frac{3 (BD)}{15 (BD)} = \frac{3}{15} = \frac{1}{5}\) of \(\displaystyle \Delta ABC\).

Example Question #1 : 2 Dimensional Geometry

Right_triangle

Note: Figure NOT drawn to scale.

Refer to the above diagram. Give the ratio of the area of \(\displaystyle \Delta BDC\) to that of \(\displaystyle \Delta ADB\).

Possible Answers:

Insufficient information is given to answer the question.

\(\displaystyle 4 :1\)

\(\displaystyle 3:1\)

\(\displaystyle 2:1\)

\(\displaystyle 5:2\)

Correct answer:

\(\displaystyle 4 :1\)

Explanation:

\(\displaystyle BD\), as the length of the altitude corresponding to the hypotenuse, is the geometric mean of the lengths of the parts of the hypotenuse it forms; that is, it is the square root of the product of the two:

\(\displaystyle BD =\sqrt{ \left ( AD\right ) \left ( DC\right )} = \sqrt{6 \cdot 24} = \sqrt{144} = 12\).

The areas of \(\displaystyle \Delta BDC\) and \(\displaystyle \Delta ADB\), each being right, are half the products of their legs, so:

The area of \(\displaystyle \Delta ADB\) is \(\displaystyle \frac{1}{2} \times (AD) (BD) = \frac{1}{2} \times 6 \times (BD)= 3(BD)\)

The area of \(\displaystyle \Delta BDC\) is \(\displaystyle \frac{1}{2} \times (CD) (BD) = \frac{1}{2} \times 24 \times (BD)= 12(BD)\)

The ratio of the areas is \(\displaystyle \frac{12 (BD)}{3 (BD)} = \frac{12 }{3 } =\frac{4}{1}\) - that is, 4 to 1.

Example Question #3 : Geometry

Thingy

Note: figure NOT drawn to scale.

Refer to the above figure. Quadrilateral \(\displaystyle BCDE\) is a square. What is the area of Polygon \(\displaystyle ABCDE\)?

Possible Answers:

\(\displaystyle 109\)

\(\displaystyle 189\)

Insufficient information is given to calculate the area.

\(\displaystyle 149\)

\(\displaystyle 139\)

Correct answer:

\(\displaystyle 109\)

Explanation:

Polygon \(\displaystyle ABCDE\) is a composite of \(\displaystyle \Delta ABE\) and Square \(\displaystyle BCDE\); its area is the sum of the areas of the two figures.

\(\displaystyle \Delta ABE\) is a right triangle; its area is half the product of its legs, which is 

\(\displaystyle A = \frac{1}{2} \cdot 5 \cdot 8 = 20\)

\(\displaystyle \overline{BE }\) is both one side of Square \(\displaystyle BCDE\) and the hypotenuse of \(\displaystyle \Delta ABE\);  its hypotenuse can be calculated from the lengths of the legs using the Pythagorean Theorem:

\(\displaystyle BE = \sqrt{5^{2}+8^{2}} = \sqrt{25 + 64 } = \sqrt{89}\).

Square \(\displaystyle BCDE\) has area the square of this, which is 89.

Polygon \(\displaystyle ABCDE\) has as its area the sum of these two areas:

\(\displaystyle 20 + 89 = 109\).

Example Question #1 : Area

Find the area of a circle with a diameter of \(\displaystyle 16\).

Possible Answers:

\(\displaystyle 81\pi\)

\(\displaystyle 32\pi\)

\(\displaystyle 256\pi\)

\(\displaystyle 64\pi\)

\(\displaystyle 16\pi\)

Correct answer:

\(\displaystyle 64\pi\)

Explanation:

Write the formula for the area of a circle.

\(\displaystyle A_{circle}= \pi r^2 = \frac{\pi d^2}{4}\)

Substitute the diameter and solve.

\(\displaystyle \frac{\pi (16)^2}{4} = \frac{\pi (16)(16)}{4}=\pi (16)(4)= 64\pi\)

Example Question #3 : 2 Dimensional Geometry

Rectangle example

Figure not drawn to scale.

Find the area of the rectangle above when the perimeter is 36 in.

Possible Answers:

72 in2

70 in2

144 in2

36 in2

84 in2

Correct answer:

72 in2

Explanation:

Rectangle example

Because we know the perimeter is 36 inches, we can determine the length of side w based on the equation of the perimeter of a rectangle:

\(\displaystyle \small Perimeter= 2(length)+2(width)\)

\(\displaystyle \small 36=2(12)+2w\)

\(\displaystyle \small 36=24+2w\)

\(\displaystyle \small 12=2w\)

\(\displaystyle \small w=6\)

Side w is 6 in long.

Now that we know that side w is 6 inches long, we have everythinng we need to calculate the area of the rectangle. 

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

\(\displaystyle \small (12)(6)=72\)

The area of the rectangle is 72 in2

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

Which of the following shapes is a kite?

Shapes

Possible Answers:

\(\displaystyle D\)

\(\displaystyle C\)

\(\displaystyle B\)

\(\displaystyle A, B\)

\(\displaystyle A\)

Correct answer:

\(\displaystyle A, B\)

Explanation:

A kite is a four-sided shape with straight sides that has two pairs of sides. Each pair of adjacent sides are equal in length. A square is also considered a kite.

Learning Tools by Varsity Tutors