Question 379 of 480
Simplify the expression \(3(x + 4) - 2(2x - 5)\). What is the result?
- \(x + 22\)
- \(-x + 22\)
- \(-x + 10\)
- \(x + 10\)
Correct Answer:
B
Explanation
To simplify the expression \(3(x + 4) - 2(2x - 5)\), we will follow a step-by-step approach. Let's break it down:
### Step 1: Distribute the coefficients
First, we need to distribute the numbers outside the parentheses to the terms inside the parentheses.
1. For the first part, \(3(x + 4)\):
- Multiply \(3\) by \(x\): \(3 \cdot x = 3x\)
- Multiply \(3\) by \(4\): \(3 \cdot 4 = 12\)
- So, \(3(x + 4) = 3x + 12\)
2. For the second part, \(-2(2x - 5)\):
- Multiply \(-2\) by \(2x\): \(-2 \cdot 2x = -4x\)
- Multiply \(-2\) by \(-5\): \(-2 \cdot -5 = 10\) (Note that multiplying two negatives gives a positive)
- So, \(-2(2x - 5) = -4x + 10\)
### Step 2: Combine the results
Now we can combine the results from both distributions:
\[
3(x + 4) - 2(2x - 5) = (3x + 12) + (-4x + 10)
\]
### Step 3: Combine like terms
Next, we will combine the like terms (the terms that contain \(x\) and the constant terms):
1. Combine the \(x\) terms:
- \(3x - 4x = -1x\) or simply \(-x\)
2. Combine the constant terms:
- \(12 + 10 = 22\)
Putting it all together, we have:
\[
-x + 22
\]
### Final Result
Thus, the simplified expression is:
\[
-x + 22
\]
### Answer
The correct option is **B. \(-x + 22\)**.
### Explanation of Other Options
- **Option A: \(x + 22\)**: This option is incorrect because it suggests that the coefficient of \(x\) is positive, which contradicts our calculation where we found it to be \(-x\).
- **Option C: \(-x + 10\)**: This option is incorrect because it has the wrong constant term. We calculated the constant term to be \(22\), not \(10\).
- **Option D: \(x + 10\)**: This option is incorrect for the same reasons as option A; it incorrectly states the coefficient of \(x\) as positive and also has the wrong constant term.
### Common Pitfalls
- **Distributing Negatives**: A common mistake is forgetting to distribute the negative sign correctly, especially when dealing with expressions like \(-2(2x - 5)\).
- **Combining Like Terms**: Ensure that you only combine terms that are similar (i.e., \(x\) terms with \(x\) terms and constant terms with constant terms).
- **Sign Errors**: Be careful with signs when adding or subtracting terms, as they can change the outcome significantly.
### Revision Summary
- Distribute coefficients carefully to each term inside parentheses.
- Combine like terms systematically to simplify expressions.
- Pay attention to signs, especially when distributing negatives.
- Double-check your final expression to ensure all terms are accounted for correctly.