ISEE Lower Level Quantitative : How to find the area of a triangle

Study concepts, example questions & explanations for ISEE Lower Level Quantitative

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Example Questions

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

What is the area of a triangle with a base of 8 and a height of 3?

Possible Answers:

\(\displaystyle 12\)

\(\displaystyle 21\)

\(\displaystyle 18\)

\(\displaystyle 24\)

\(\displaystyle 11\)

Correct answer:

\(\displaystyle 12\)

Explanation:

The area of a triangle is \(\displaystyle \frac{1}{2}*(base* height)\). We know that our base is 8 and our height is 3.

In this case, the equation is \(\displaystyle \frac{1}{2}*(8* 3)\). Now we can solve this equation.

\(\displaystyle \frac{1}{2}(24)\)

\(\displaystyle 12\)

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

What is the area of a triangle that has a base of 7 and a height of 10?

Possible Answers:

\(\displaystyle 68\)

\(\displaystyle 17\)

\(\displaystyle 28\)

\(\displaystyle 35\)

\(\displaystyle 70\)

Correct answer:

\(\displaystyle 35\)

Explanation:

To find the area of a triangle, we use \(\displaystyle \frac{1}{2}*(base* height)\). We know the height of the triangle is 10 and the base is 7.

\(\displaystyle \frac{1}{2}*(base*height)=\frac{1}{2}*(7*10)\)

\(\displaystyle \frac{1}{2}*(70)\)

\(\displaystyle 35\)

Example Question #2 : How To Find The Area Of A Triangle

What is the area of a triangle with a base of 7cm and a height of 4cm? 

Possible Answers:

\(\displaystyle 14cm^2\)

\(\displaystyle 11cm^2\)

\(\displaystyle 28cm^2\)

\(\displaystyle 21cm^2\)

Correct answer:

\(\displaystyle 14cm^2\)

Explanation:

Use the formula for the area of a triangle

\(\displaystyle \frac{1}{2}bh\)

to solve this problem. Plug in and you get \(\displaystyle 14\ cm^{2}\).

 

Example Question #3 : How To Find The Area Of A Triangle

The height of a triangle is \(\displaystyle 6\) ft. The base is \(\displaystyle 8\) ft. What is the area of the triangle?

Possible Answers:

\(\displaystyle 6ft^{2}\)

\(\displaystyle 48ft^{2}\)

\(\displaystyle 8ft^{2}\)

\(\displaystyle 24 ft^{2}\)

Correct answer:

\(\displaystyle 24 ft^{2}\)

Explanation:

The formula for finding the area of a triangle is \(\displaystyle \frac{1}{2}(base\times height)\). Multiply the base times the height first. \(\displaystyle 8\times6=48\). Then, either multiply  \(\displaystyle \frac{1}{2}\times\frac{48}{1}\) , or simply divide \(\displaystyle 48\div2\). Therefore the answer is \(\displaystyle 24ft^{2}\).

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

A right triangle has a base of 4 and a height of 7.

What is the triangle's area?

Possible Answers:

\(\displaystyle 24\)

\(\displaystyle 28\)

\(\displaystyle 14\)

\(\displaystyle 12\)

\(\displaystyle 17\)

Correct answer:

\(\displaystyle 14\)

Explanation:

An area of a triangle is

\(\displaystyle \frac{1}{2}\times base\times height\)

In this case

\(\displaystyle \frac{1}{2}\times 4\times 7=14\)

Example Question #6 : How To Find The Area Of A Triangle

If the base of a triangle is 12 cm, and the height of the triangle is 4 cm, what is the total area of the triangle?

Possible Answers:

\(\displaystyle 96\ cm^2\)

 

\(\displaystyle 24\ cm^2\)

\(\displaystyle 16\ cm^2\)

\(\displaystyle 36\ cm^2\)

\(\displaystyle 48\ cm^2\)

Correct answer:

\(\displaystyle 24\ cm^2\)

Explanation:

First, you must remember the formula for the area of a triangle \(\displaystyle (A=\frac{1}{2}bh)\).

Plug in the given values: \(\displaystyle A=\frac{1}{2}(4)(12)\).

Multiply to get 24. Since this is area, the units must be sqaured. Therefore, your final answer is \(\displaystyle 24\ cm^2\).

Example Question #5 : How To Find The Area Of A Triangle

What is the area of the right triangle in the following figure?

1

Possible Answers:

\(\displaystyle 80\textup{ in}^2\)

\(\displaystyle 81.5\textup{ in}^2\)

\(\displaystyle 58.5\textup{ in}^2\)

\(\displaystyle 117\textup{ in}^2\)

\(\displaystyle 65.5\textup{ in}^2\)

Correct answer:

\(\displaystyle 58.5\textup{ in}^2\)

Explanation:

There are several different ways to solve for the area of a right triangle. In this lesson, we will transform the right triangle into a rectangle, use the the simpler formula for area of a rectangle to solve for the new figure's area, and divide this area in half in order to solve for the area of the original figure.

First, let's transform the triangle into a rectangle:

1 1

Second, let's remember that the formula for area of a rectangle is  as follows:

\(\displaystyle A=l\times w\)

Substitute in our side lengths.

\(\displaystyle A=13\times 9\)

\(\displaystyle A=117\)

Last, notice that our triangle is exactly half the size of the rectangle that we made. This means that in order to solve for the area of the triangle we will need to take half of the area of the rectangle, or divide it by \(\displaystyle 2\).

\(\displaystyle 117\div 2= 58.5\textup{ in}^2\)

Thus, the area formula for a right triangle is as follows:

\(\displaystyle A=\frac{1}{2}(l\times w)\) or \(\displaystyle A=\frac{l\times w}{2}\)

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

What is the area of the right triangle in the following figure?

2

Possible Answers:

\(\displaystyle 30\textup{ in}^2\)

\(\displaystyle 48\textup{ in}^2\)

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

\(\displaystyle 45.5\textup{ in}^2\)

\(\displaystyle 36.5\textup{ in}^2\)

Correct answer:

\(\displaystyle 48\textup{ in}^2\)

Explanation:

There are several different ways to solve for the area of a right triangle. In this lesson, we will transform the right triangle into a rectangle, use the the simpler formula for area of a rectangle to solve for the new figure's area, and divide this area in half in order to solve for the area of the original figure.

First, let's transform the triangle into a rectangle:

 2 1

Second, let's remember that the formula for area of a rectangle is  as follows:

\(\displaystyle A=l\times w\)

Substitute in our side lengths.

\(\displaystyle A=12\times 8\)

\(\displaystyle A=96\)

Last, notice that our triangle is exactly half the size of the rectangle that we made. This means that in order to solve for the area of the triangle we will need to take half of the area of the rectangle, or divide it by \(\displaystyle 2\).

\(\displaystyle 96\div 2= 48\textup{ in}^2\)

Thus, the area formula for a right triangle is as follows:

\(\displaystyle A=\frac{1}{2}(l\times w)\) or \(\displaystyle A=\frac{l\times w}{2}\)

Example Question #1 : Find Area Of Polygons: Ccss.Math.Content.6.G.A.1

What is the area of the right triangle in the following figure?

3

Possible Answers:

\(\displaystyle 60\textup{ in}^2\)

\(\displaystyle 52.5\textup{ in}^2\)

\(\displaystyle 63\textup{ in}^2\)

\(\displaystyle 49.5\textup{ in}^2\)

\(\displaystyle 58.5\textup{ in}^2\)

Correct answer:

\(\displaystyle 49.5\textup{ in}^2\)

Explanation:

There are several different ways to solve for the area of a right triangle. In this lesson, we will transform the right triangle into a rectangle, use the the simpler formula for area of a rectangle to solve for the new figure's area, and divide this area in half in order to solve for the area of the original figure.

First, let's transform the triangle into a rectangle:

 3 3

Second, let's remember that the formula for area of a rectangle is  as follows:

\(\displaystyle A=l\times w\)

Substitute in our side lengths.

\(\displaystyle A=11\times 9\)

\(\displaystyle A=99\)

Last, notice that our triangle is exactly half the size of the rectangle that we made. This means that in order to solve for the area of the triangle we will need to take half of the area of the rectangle, or divide it by \(\displaystyle 2\).

\(\displaystyle 99\div 2= 49.5\textup{ in}^2\)

Thus, the area formula for a right triangle is as follows:

\(\displaystyle A=\frac{1}{2}(l\times w)\) or \(\displaystyle A=\frac{l\times w}{2}\)

Example Question #6 : How To Find The Area Of A Triangle

What is the area of the right triangle in the following figure?

4

Possible Answers:

\(\displaystyle 30.5\textup{ in}^2\)

\(\displaystyle 43\textup{ in}^2\)

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

\(\displaystyle 35\textup{ in}^2\)

\(\displaystyle 40.5\textup{ in}^2\)

Correct answer:

\(\displaystyle 35\textup{ in}^2\)

Explanation:

There are several different ways to solve for the area of a right triangle. In this lesson, we will transform the right triangle into a rectangle, use the the simpler formula for area of a rectangle to solve for the new figure's area, and divide this area in half in order to solve for the area of the original figure.

First, let's transform the triangle into a rectangle:

4 4 

Second, let's remember that the formula for area of a rectangle is  as follows:

\(\displaystyle A=l\times w\)

Substitute in our side lengths.

\(\displaystyle A=10\times 7\)

\(\displaystyle A=70\)

Last, notice that our triangle is exactly half the size of the rectangle that we made. This means that in order to solve for the area of the triangle we will need to take half of the area of the rectangle, or divide it by \(\displaystyle 2\).

\(\displaystyle 70\div 2= 35\textup{ in}^2\)

Thus, the area formula for a right triangle is as follows:

\(\displaystyle A=\frac{1}{2}(l\times w)\) or \(\displaystyle A=\frac{l\times w}{2}\)

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