Algebra · real student question

Solve the inequality (2x - 1)/3 > (3x - 5)/4 and write the solution set.

Question

Solve the inequality

2x13>3x54\frac{2x-1}{3}>\frac{3x-5}{4}

and write the solution set.

Step-by-step solution

  1. Clear the fractions with the least common denominator. The denominators are 33 and 44, so the LCD is 1212. Multiplying both sides of an inequality by a positive number keeps the direction of the inequality, and 12>012>0, so nothing flips:

    122x13>123x54    4(2x1)>3(3x5).12\cdot\frac{2x-1}{3}>12\cdot\frac{3x-5}{4}\;\Longrightarrow\;4(2x-1)>3(3x-5).

    This single move is why fraction inequalities are no harder than integer ones — get rid of the denominators first, before touching the xx terms.

  2. Distribute on both sides. Expanding each product:

    4(2x1)=8x4,3(3x5)=9x15,4(2x-1)=8x-4,\qquad 3(3x-5)=9x-15,

    so the inequality becomes

    8x4>9x15.8x-4>9x-15.

    Watch the 3×(5)=+15-3\times(-5)=+15 sign: dropping that minus is the most common error in this step, and it changes the final boundary from 1111 to 19-19.

  3. Collect the xx terms on the side that keeps the coefficient positive. Subtracting 8x8x from both sides leaves the xx on the right:

    4>x15.-4>x-15.

    You could instead subtract 9x9x and get x4>15-x-4>-15, but then you would have to divide by 1-1 and remember to reverse the inequality. Moving the smaller coefficient avoids that trap entirely.

  4. Isolate xx and read off the solution. Adding 1515 to both sides:

    11>x,that isx<11.11>x,\qquad\text{that is}\qquad x<11.

    In interval notation the solution set is (,11)(-\infty,11). Note 1111 itself is excluded because the original inequality is strict.

  5. Test one value inside and one outside. At x=10.9x=10.9: left side =20.836.933=\frac{20.8}{3}\approx 6.933, right side =27.74=6.925=\frac{27.7}{4}=6.925, and 6.933>6.9256.933>6.925 ✓. At x=11.1x=11.1: left 7.067\approx 7.067, right =7.075=7.075, so the inequality fails ✓. The boundary x=11x=11 makes both sides equal 77, confirming it is exactly the cut-off.

Answer

x<11or, in interval notation,(,11)x<11\quad\text{or, in interval notation,}\quad(-\infty,\,11)

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