Question

Difficulty: MediumLinear and Quadratic Inequalities

What is the solution set for the linear inequality 1−4x3≤x+72\frac{1 - 4x}{3} \le \frac{x + 7}{2}?

  1. x≥−1911x \ge -\frac{19}{11}Answer
  2. B
    x≤−1911x \le -\frac{19}{11}
  3. C
    x≥1911x \ge \frac{19}{11}
  4. D
    x≤235x \le \frac{23}{5}

Answer

x≥−1911x \ge -\frac{19}{11}
Multiplying the inequality by 6 clears denominators to give 2(1−4x)≤3(x+7)2(1 - 4x) \le 3(x + 7). Expanding gives 2−8x≤3x+212 - 8x \le 3x + 21, which simplifies to −11x≤19-11x \le 19. Dividing both sides by −11-11 flips the inequality sign, yielding x≥−1911x \ge -\frac{19}{11}.

Step-by-Step Solution

1
Clear the denominators by multiplying both sides of the inequality by the lowest common multiple of 3 and 2, which is 6.
6⋅(1−4x3)≤6⋅(x+72)  ⟹  2(1−4x)≤3(x+7)6 \cdot \left(\frac{1 - 4x}{3}\right) \le 6 \cdot \left(\frac{x + 7}{2}\right) \implies 2(1 - 4x) \le 3(x + 7)
Eliminating fractions simplifies the algebraic manipulation.
2
Expand both sides by distributing the factors.
2−8x≤3x+212 - 8x \le 3x + 21
Removing parentheses allows grouping of like terms.
3
Rearrange terms by collecting terms containing xx on the left and constants on the right.
−8x−3x≤21−2  ⟹  −11x≤19-8x - 3x \le 21 - 2 \implies -11x \le 19
Isolating the variable term prepares for the final division step.
4
Divide both sides by −11-11 and reverse the direction of the inequality sign.
x≥−1911x \ge -\frac{19}{11}
Dividing or multiplying an inequality by a negative real number requires flipping the inequality sign.

Key Concept

Solving linear inequalities involving fractions and reversing the inequality sign when dividing by a negative number.
Estimated Time:1m 30s
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