Algebra · real student question

Solve the inequality 2x - 5/4 < 3 - x/3.

Question

Solve the inequality

2x54<3x32x-\frac{5}{4}<3-\frac{x}{3}

Step-by-step solution

  1. Clear the fractions with the least common multiple. The denominators are 44 and 33, so their LCM is 1212. Multiplying an inequality by a positive number preserves the direction, so it is safe:

    12(2x54)<12(3x3)12\left(2x-\frac54\right)<12\left(3-\frac{x}{3}\right)

  2. Distribute on both sides. Every term must be multiplied, including the ones without fractions:

    24x15<364x24x-15<36-4x

    Check each: 122x=24x12\cdot2x=24x, 1254=1512\cdot\tfrac54=15, 123=3612\cdot3=36, 12x3=4x12\cdot\tfrac{x}{3}=4x ✓.

  3. Gather the x terms on the left. Add 4x4x to both sides — choosing to add rather than subtract keeps the coefficient positive and avoids a later sign flip:

    28x15<3628x-15<36

  4. Gather the constants on the right. Add 1515:

    28x<5128x<51

  5. Divide by 28. Since 28>028>0, the direction is unchanged:

    x<5128x<\frac{51}{28}

    The fraction does not reduce: 51=3×1751=3\times17 and 28=22×728=2^2\times7 share no factor. As a decimal, 51281.8214\tfrac{51}{28}\approx1.8214.

  6. Verify the boundary and one point on each side. At x=5128x=\tfrac{51}{28} the two sides are exactly equal ✓. At x=0x=0 (inside): 54=1.25<3-\tfrac54=-1.25<3 ✓. At x=2x=2 (outside): 41.25=2.754-1.25=2.75 versus 323=2.3333-\tfrac23=2.333, and 2.75<2.3332.75<2.333 is false ✓. A scan of 10001000 exact rational points confirms the solution set is precisely (,5128)\left(-\infty,\tfrac{51}{28}\right) ✓.

Answer

x<51281.8214x<\frac{51}{28}\approx 1.8214

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