JAMB 2019 Mathematics · Question 17

Solve for x in 4x−63≤3+2x2\frac{4x - 6}{3} \leq \frac{3 + 2x}{2}

Options

  1. A.x≤112x \leq 1\frac{1}{2}
  2. B.x≤212x \leq \frac{21}{2}
  3. C.x≥212x \geq \frac{21}{2}
  4. D.x≥112x \geq 1\frac{1}{2}

Answer: B. x≤212x \leq \frac{21}{2}

Explanation written with AI and checked against the answer key

Analysis

To solve this linear inequality, we need to eliminate the fractions by finding a common denominator and then isolate the variable xx.

Concept

When dealing with inequalities involving fractions, the most efficient method is to multiply the entire inequality by the Least Common Multiple (LCM) of the denominators. In this case, the denominators are 3 and 2, so the LCM is 6.

Important Rule: When multiplying or dividing an inequality by a negative number, you must reverse the inequality sign. Since we are multiplying by a positive 6, the sign remains the same.

Step-by-Step Solution

Step 1: Multiply both sides by 6 to clear the fractions.

6×(4x−63)≤6×(3+2x2)6 \times \left( \frac{4x - 6}{3} \right) \leq 6 \times \left( \frac{3 + 2x}{2} \right)

Step 2: Simplify the expression.

2(4x−6)≤3(3+2x)2(4x - 6) \leq 3(3 + 2x)

Step 3: Expand the brackets.

8x−12≤9+6x8x - 12 \leq 9 + 6x

Step 4: Group the xx terms on one side and the constants on the other. Subtract 6x6x from both sides:

8x−6x−12≤98x - 6x - 12 \leq 9
2x−12≤92x - 12 \leq 9

Add 12 to both sides:

2x≤9+122x \leq 9 + 12
2x≤212x \leq 21

Step 5: Solve for xx. Divide both sides by 2:

x≤212x \leq \frac{21}{2}

Or, in mixed fraction form:

x≤1012x \leq 10\frac{1}{2}
Conclusion

Comparing our result (x≤212x \leq \frac{21}{2}) with the provided options, it matches option B.

Exam Tip

Always check your answer by picking a number that satisfies your result. For example, if x=0x = 0 (which is ≤10.5\leq 10.5), the original inequality becomes −63≤32\frac{-6}{3} \leq \frac{3}{2}, which is −2≤1.5-2 \leq 1.5. Since this is true, your solution is likely correct!

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