1. **State the problem:** Solve the equation $$12 \times \frac{120}{n + 5} = 12 \times \frac{120}{n} - 24$$ for $n$.
2. **Write the equation clearly:**
$$12 \cdot \frac{120}{n + 5} = 12 \cdot \frac{120}{n} - 24$$
3. **Simplify the terms:**
$$\frac{1440}{n + 5} = \frac{1440}{n} - 24$$
4. **Isolate terms and clear denominators:** Multiply both sides by $n(n+5)$ to eliminate fractions:
$$n(n+5) \times \frac{1440}{n + 5} = n(n+5) \times \left(\frac{1440}{n} - 24\right)$$
5. **Cancel common factors:**
$$\cancel{n}(n+5) \times \frac{1440}{\cancel{n} + 5} = n \cancel{(n+5)} \times \frac{1440}{n} - 24 n (n+5)$$
which simplifies to
$$1440 n = 1440 (n+5) - 24 n (n+5)$$
6. **Expand the right side:**
$$1440 n = 1440 n + 7200 - 24 n^2 - 120 n$$
7. **Bring all terms to one side:**
$$1440 n - 1440 n - 7200 + 24 n^2 + 120 n = 0$$
which simplifies to
$$24 n^2 + 120 n - 7200 = 0$$
8. **Divide entire equation by 24 to simplify:**
$$\frac{24 n^2}{24} + \frac{120 n}{24} - \frac{7200}{24} = 0$$
$$n^2 + 5 n - 300 = 0$$
9. **Solve quadratic equation:**
Use the quadratic formula:
$$n = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$$
where $a=1$, $b=5$, $c=-300$.
10. **Calculate discriminant:**
$$\Delta = 5^2 - 4 \times 1 \times (-300) = 25 + 1200 = 1225$$
11. **Find square root of discriminant:**
$$\sqrt{1225} = 35$$
12. **Calculate roots:**
$$n = \frac{-5 \pm 35}{2}$$
13. **Find each solution:**
- $$n = \frac{-5 + 35}{2} = \frac{30}{2} = 15$$
- $$n = \frac{-5 - 35}{2} = \frac{-40}{2} = -20$$
14. **Check for restrictions:**
Denominators $n$ and $n+5$ cannot be zero, so $n \neq 0$ and $n \neq -5$.
Both solutions $15$ and $-20$ are valid.
**Final answer:**
$$n = 15 \text{ or } n = -20$$
Solve Rational Equation E28436
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