ACT Math : ACT Math

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #111 : Rectangles

The sides of rectangle ABCD are 4 in and 13 in. 

How long is the diagonal of rectangle ABCD?

Possible Answers:

\(\displaystyle 185\)

\(\displaystyle 52\)

\(\displaystyle \sqrt{185}\)

\(\displaystyle \sqrt{125}\)

\(\displaystyle 17\)

Correct answer:

\(\displaystyle \sqrt{185}\)

Explanation:

A diagonal of a rectangle cuts the rectangle into 2 right triangles with sides equal to the sides of the rectangle and with a hypotenuse that is the diagonal. All you need to do is use the pythagorean theorem:

\(\displaystyle a^2+b^2=c^2\) where a and b are the sides of the rectangle and c is the length of the diagonal. 

\(\displaystyle \sqrt{4^2+16^2}=\sqrt{185}=c\)

Example Question #1 : How To Find The Length Of The Diagonal Of A Rectangle

A power company needs to run a piece of wire across a rectangular plot of land and must do so diagonally.  The land is \(\displaystyle 6\) \(\displaystyle \textup{miles}\) by \(\displaystyle 2\) \(\displaystyle \textup{miles}\) in measurement. If it costs \(\displaystyle \$15250\)  for each mile of wire deployed, how much is the expected cost of this project?  Round to the nearest cent.

Possible Answers:

\(\displaystyle \$96449.47\)

\(\displaystyle \$183000\)

\(\displaystyle \$157429.14\)

\(\displaystyle \$144250.5\)

\(\displaystyle \$122000\)

Correct answer:

\(\displaystyle \$96449.47\)

Explanation:

Notice that this problem could be represented as follows:

Rect62

This means that you can find the distance of the wire merely by using the Pythagorean theorem:

\(\displaystyle 6^2+2^2=c^2\)

Solving for \(\displaystyle c\), you get:

\(\displaystyle c^2 = 36+4\)

\(\displaystyle c^2 = 40\)

Thus, \(\displaystyle c=\sqrt{40}\)

Using your calculator, multiply this by \(\displaystyle 15250\).  This gives you approximately \(\displaystyle 96449.47\) dollars in expenses.

Example Question #2 : How To Find The Length Of The Diagonal Of A Rectangle

What is the diagonal of a rectangle with sides of length \(\displaystyle 12\) and \(\displaystyle 3\)? Round to the nearest hundredth.

Possible Answers:

\(\displaystyle 14.84\)

\(\displaystyle 14.13\)

\(\displaystyle 13.58\)

\(\displaystyle 13\)

\(\displaystyle 12.37\)

Correct answer:

\(\displaystyle 12.37\)

Explanation:

You could draw this rectangle as follows:

Rect212

Solving for the diagonal merely requires using the Pythagorean theorem. Thus, you know:

\(\displaystyle 3^2+12^2=c^2\) or 

\(\displaystyle 9+144=c^2\)

\(\displaystyle c^2=153\), meaning that \(\displaystyle c=\sqrt{153}\)

This is approximately \(\displaystyle 12.36931687685298...\) Thus, the answer is \(\displaystyle 12.37\).

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

What is the area of a rectangle with a diagonal of \(\displaystyle 15\) \(\displaystyle \textup{in}\) and one side that is \(\displaystyle 9\) \(\displaystyle \textup{in}\)?

Possible Answers:

\(\displaystyle 104\) \(\displaystyle \textup{in}^{2}\)

\(\displaystyle 12\) \(\displaystyle \textup{in}^{2}\)

\(\displaystyle 108\) \(\displaystyle \textup{in}^{2}\)

\(\displaystyle 42\) \(\displaystyle \textup{in}^{2}\)

\(\displaystyle 45\) \(\displaystyle \textup{in}^{2}\)

Correct answer:

\(\displaystyle 108\) \(\displaystyle \textup{in}^{2}\)

Explanation:

Based on the description offered in the question, you know that your rectangle must look something like this:

Rect15hyp

Using the Pythagorean theorem, you can solve for the unknown side \(\displaystyle x\):

\(\displaystyle 9^2+x^2=15^2\)

\(\displaystyle 81+x^2=225\)

\(\displaystyle x^2=144\)

Thus, \(\displaystyle x\) is \(\displaystyle 12\).  This means that the area is \(\displaystyle 9*12\) or \(\displaystyle 108\) \(\displaystyle \textup{in}^{2}\).

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

Mark bought a TV at the store that was listed as 36in x 24in. He needs to figure out the diagonal to make sure the television is large enough but he left his measuring tape at his mother's house. What is the diagonal length of this television's screen in terms of inches?

Possible Answers:

\(\displaystyle 60 in\)

\(\displaystyle 43.3in\)

\(\displaystyle 38.3 in\)

\(\displaystyle 30 in\)

Correct answer:

\(\displaystyle 43.3in\)

Explanation:

Finding the diagonal of a rectangle is essentially a problem with triangles. If we set up a right triangle with legs 24 in. and 36 in., and set \(\displaystyle d\) to be the diagonal (the hypotenuse), we can use the Pythagorean Theorem to solve for \(\displaystyle d\):

\(\displaystyle {} 24^2+36^2=d^2\)

\(\displaystyle {} d=\sqrt{1872}\)

This comes out to be about 43.3 in.

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

The width, in cm, of a rectangular fence is 2 more than half its length, in cm. Which of the following gives the width, w cm, in terms of length, l cm, of the rectangular fence?

Possible Answers:

w = 2l – 2

w = ½ l – 2

w = 2l + 2

w = ½ l + 2

Correct answer:

w = ½ l + 2

Explanation:

To find the width, we must take half of the length, which means we must divide the length by 2. Then we must take 2 more than that number, which means we must add 2 to the number. Combining these, we get:

w = ½ l + 2

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

 

The width of a rectangle is 2 inches longer than 3 times its length.  Which of the following equations gives the width, w, of the rectangle in terms of its length, l,?

 

 

Possible Answers:

w = 6l +2

w = 3l + 2

w = 3l – 2

w = 1/3l +2

Correct answer:

w = 3l + 2

Explanation:

The width equals 3 times the length, so 3l, plus an additional two inches, so + 2, = 3l + 2

 

 

 

Example Question #201 : Geometry

Your dad shows you a rectangular scale drawing of your house. The drawing is 6 inches by 8 inches. You're trying to figure out the actual length of the shorter side of the house. If you know the actual length of the longer side is 64 feet, what is the actual length of the shorter side of the house (in feet)?

Possible Answers:

36

81

32

48

60

Correct answer:

48

Explanation:

We can solve this by setting up a proportion and solving for x,the length of the shorter side of the house. If the drawing is scale and is 6 : 8, then the actual house is x : 64. Then we can cross multiply so that 384 = 8x. We then divide by 8 to get x = 48. 

Example Question #1 : Rectangles

What is the perimeter of the below rectangle in simplest radical form?

 

                                     Act_math_159_15

Possible Answers:

7√27

10√3

4√3 + 2√27

5√3

Correct answer:

10√3

Explanation:

The perimeter of a figure is the sum of the lengths of all of its sides. The perimeter of this figure is √27 + 2√3 + √27 + 2√3. But, √27 = √9√3 = 3√3 . Now all of the sides have the same number underneath of the radical symbol (i.e. the same radicand) and so the coefficients of each radical can be added together. The result is that the perimeter is equal to 10√3.

 

 

Example Question #1 : How To Find The Perimeter Of A Rectangle

A rectangle has an area of 56 square feet, and a width of 4 feet. What is the perimeter, in feet, of the rectangle?

Possible Answers:
14
120
30
28
36
Correct answer: 36
Explanation:

Divide the area of the rectangle by the width in order to find the length of 14 feet. The perimeter is the sum of the side lengths, which in this case is 14 feet + 4 feet +14 feet + 4 feet, or 36 feet.

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