JAMB 2011 Mathematics · Question 15

Solve the inequality -6(x + 3) ≤\leq 4(x - 2)

Options

  1. A.x ≤\leq 2
  2. B.x ≥\geq -1
  3. C.x ≥\geq -2
  4. D.x ≤\leq -1

Answer: B. x ≥\geq -1

Explanation written with AI and checked against the answer key

Analysis

To solve the inequality −6(x+3)≤4(x−2)-6(x + 3) \leq 4(x - 2), we need to expand the brackets, collect like terms, and isolate the variable xx. A crucial rule to remember is that when you divide or multiply an inequality by a negative number, the inequality sign must be reversed.

Concept
  1. Expansion: Use the distributive property to remove the brackets.
  2. Grouping: Move all terms containing xx to one side and constant terms to the other.
  3. Division: Divide by the coefficient of xx. If the coefficient is negative, flip the inequality sign (≤\leq becomes ≥\geq).
Step-by-Step Solution

Step 1: Expand the brackets −6×x−6×3≤4×x−4×2-6 \times x - 6 \times 3 \leq 4 \times x - 4 \times 2 −6x−18≤4x−8-6x - 18 \leq 4x - 8

Step 2: Collect like terms Move 4x4x to the left side and −18-18 to the right side: −6x−4x≤−8+18-6x - 4x \leq -8 + 18

Step 3: Simplify both sides −10x≤10-10x \leq 10

Step 4: Solve for xx Divide both sides by −10-10. Because we are dividing by a negative number, the inequality sign ≤\leq changes to ≥\geq: x≥10−10x \geq \frac{10}{-10} x≥−1x \geq -1

Conclusion

Comparing our result (x≥−1x \geq -1) with the given options, it matches option B.

Exam Tip: Always double-check your sign when dividing by a negative number! Many students lose marks here by forgetting to flip the inequality sign. If you are ever unsure, pick a number that satisfies your final answer (e.g., x=0x = 0) and plug it back into the original equation to see if it holds true.

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