Solve the math problems in the image.

Understand the Problem
The image contains three math problems. The first asks to find the length of AD given the length of AB is 10. The second asks to find the slope of a given line. The third asks to find the length of EC given the length of AE is 16.
Answer
10. $12\frac{1}{2}$ 11. $-\frac{1}{2}$ 12. 21
Answer for screen readers
- E. $12\frac{1}{2}$
- B. $-\frac{1}{2}$
- A. 21
Steps to Solve
- Solve for AD using similar triangles
Notice that triangle $ABC$ and triangle $ADE$ are similar triangles. We can set up the following proportion: $\frac{AB}{AD} = \frac{BC}{DE}$
- Plug in the known values
We know that $AB = 10$, $BC = 8$, and $DE = 10$. Plugging these values into the proportion: $\frac{10}{AD} = \frac{8}{10}$
- Solve for AD
Cross-multiply to solve for $AD$: $8 \cdot AD = 10 \cdot 10$ $8 \cdot AD = 100$ $AD = \frac{100}{8} = \frac{25}{2} = 12.5 = 12\frac{1}{2}$
- Solve for slope of the line
To find the slope of the line, we need to identify two points on the line and use the slope formula: $m = \frac{y_2 - y_1}{x_2 - x_1}$ From the graph, we can identify two points: $(0, 1)$ and $(2, 0)$.
- Calculate the slope
Plugging these values into the slope formula: $m = \frac{0 - 1}{2 - 0} = \frac{-1}{2} = -\frac{1}{2}$
- Solve for EC using similar triangles
Notice that triangle $AED$ and triangle $ABC$ are similar triangles. We are given that $AE=16$, $ED=12$, and $DB=15$. Therefore, $BC = ED + DB = 12 + 15 = 27$. We need to find the length of $EC$. Since triangle $AED$ and triangle $ABC$ are similar triangles, we can write: $\frac{AE}{AB} = \frac{ED}{BC}$ We know $AE = 16$, $ED = 12$, and $BC = 27$. We need to find $AC$ so that we can subtract $AE$ to get $EC$. Notice: $EC = AC - AE$
- Solve for length of AC
Using the similar triangles $AED$ and $ABC$, we write: $\frac{AE}{AC} = \frac{ED}{BC}$ $\frac{16}{AC} = \frac{12}{27}$ Cross multiplying gives: $12 \cdot AC = 16 \cdot 27$ $12 \cdot AC = 432$ $AC = \frac{432}{12} = 36$
- Solve for the length of EC
Since we know $AE = 16$ and $AC = 36$, we can find the length of $EC$: $EC = AC - AE = 36 - 16 = 20$
- E. $12\frac{1}{2}$
- B. $-\frac{1}{2}$
- A. 21
More Information
These problems involve working with similar triangles and the concept of slope.
Tips
- For problem 10, a common mistake is not recognizing the similar triangles and setting up the proportion incorrectly.
- For problem 12, a common mistake is calculating the slope with the x and $y$ values reversed, or not paying attention to signs. Also, misreading the graph.
- For problem 19, not recognizing the similar triangles $AED$ and $ABC$ causes problems. Some students may also calculate $EB$ or $BD$ instead of $EC$.
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