Question: Spiral Review
Problems 8–11: Evaluate each expression.
8. -5 • (-2.4)
9. -7.4 ÷ 10
10. -4/7 ÷ (-2)
11. 4 • (-3/8)
12. Select all of the expressions that have a negative value.
A. -11/8
B. -11/8
C. 11/-8
D. -11/-8
E. 11/8
1. **State the problem:** Evaluate each expression from problems 8 to 11 and identify which expressions in problem 12 have negative values.
2. **Recall the rules:**
- Multiplying two numbers with the same sign gives a positive result.
- Multiplying two numbers with different signs gives a negative result.
- Dividing follows the same sign rules as multiplication.
- Fractions can be treated as division.
3. **Problem 8:** Evaluate $$-5 \times (-2.4)$$
- Both numbers are negative, so the product is positive.
- Calculate $$5 \times 2.4 = 12$$
- Therefore, $$-5 \times (-2.4) = 12$$
4. **Problem 9:** Evaluate $$-7.4 \div 10$$
- Dividing a negative by a positive gives a negative.
- Calculate $$7.4 \div 10 = 0.74$$
- Therefore, $$-7.4 \div 10 = -0.74$$
5. **Problem 10:** Evaluate $$\frac{-4}{7} \div (-2)$$
- Division of fractions: $$\frac{a}{b} \div c = \frac{a}{b} \times \frac{1}{c}$$
- So, $$\frac{-4}{7} \div (-2) = \frac{-4}{7} \times \frac{1}{-2}$$
- Multiply numerators and denominators:
$$\frac{-4 \times 1}{7 \times -2} = \frac{-4}{-14}$$
- Cancel negatives: $$\frac{\cancel{-4}}{\cancel{-14}} = \frac{4}{14}$$
- Simplify fraction: $$\frac{4}{14} = \frac{2}{7}$$
- Therefore, $$\frac{-4}{7} \div (-2) = \frac{2}{7}$$
6. **Problem 11:** Evaluate $$4 \times \left(-\frac{3}{8}\right)$$
- Multiply numerator: $$4 \times -3 = -12$$
- Denominator remains 8
- So, $$4 \times \left(-\frac{3}{8}\right) = \frac{-12}{8}$$
- Simplify fraction by dividing numerator and denominator by 4:
$$\frac{\cancel{-12}}{\cancel{8}} = \frac{-3}{2}$$
- Therefore, $$4 \times \left(-\frac{3}{8}\right) = -\frac{3}{2}$$
7. **Problem 12:** Identify which expressions have negative values.
- A. $$-\frac{11}{8}$$ is negative.
- B. $$-\frac{11}{8}$$ is negative (same as A).
- C. $$\frac{11}{-8}$$ is negative (negative denominator).
- D. $$-\frac{11}{-8}$$ is positive (negative numerator and denominator cancel).
- E. $$\frac{11}{8}$$ is positive.
**Final answers:**
- 8: $$12$$
- 9: $$-0.74$$
- 10: $$\frac{2}{7}$$
- 11: $$-\frac{3}{2}$$
- 12: Expressions A, B, and C have negative values.