JAMB 2025 Mathematics · Question 52

Solve the inequality 2x + 3 > 5x + 8

Options

  1. A.x > 123\frac{2}{3}
  2. B.x > -123\frac{2}{3}
  3. C.x < -123\frac{2}{3}
  4. D.x < 123\frac{2}{3}

Answer: C. x < -123\frac{2}{3}

Explanation written with AI and checked against the answer key

Analysis

The goal is to solve for xx in the linear inequality 2x+3>5x+82x + 3 > 5x + 8. Solving an inequality is very similar to solving an equation, but you must be careful when multiplying or dividing by a negative number, as that flips the inequality sign.

Concept

To solve this, we need to group the terms containing xx on one side and the constant terms on the other side.

Step-by-Step Solution

Step 1: Group the terms Subtract 5x5x from both sides of the inequality to bring all xx terms to the left: 2x−5x+3>82x - 5x + 3 > 8 −3x+3>8-3x + 3 > 8

Step 2: Isolate the xx term Subtract 33 from both sides: −3x>8−3-3x > 8 - 3 −3x>5-3x > 5

Step 3: Solve for xx Divide both sides by −3-3. Important Rule: Whenever you divide or multiply an inequality by a negative number, you must reverse the inequality sign (>> becomes <<).

x<5−3x < \frac{5}{-3}

Step 4: Simplify the fraction x<−53x < -\frac{5}{3}

Converting the improper fraction to a mixed fraction: 5÷3=15 \div 3 = 1 remainder 22 So, x<−123x < -1\frac{2}{3}

Conclusion

Comparing our result (x<−123x < -1\frac{2}{3}) with the given options, it matches option C.

Exam Tip

Always double-check your inequality sign when dealing with negative coefficients. A common mistake in JAMB is forgetting to flip the sign when dividing by a negative number, which would lead you to choose the wrong direction (like option B).

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