Algebra · real student question

Solve the compound inequality 16 < 3y - 8 <= 40.

Question

Solve the compound inequality

16<3y84016<3y-8\le 40

Step-by-step solution

  1. Read the statement as two conditions joined by "and". The chain 16<3y84016<3y-8\le40 says 16<3y816<3y-8 and 3y8403y-8\le40 hold at once. Rather than splitting them, you can operate on all three parts simultaneously — that is exactly what a chained inequality allows.

  2. Undo the subtraction first by adding 8 to every part. Adding the same number to all three parts shifts the whole chain and cannot flip any sign:

    16+8<3y8+840+816+8<3y-8+8\le 40+8

    24<3y4824<3y\le 48

  3. Divide every part by 3 to isolate yy. The divisor 33 is positive, so the directions of both inequality signs are preserved — this is the step where a negative coefficient would have forced a reversal:

    243<3y3483\frac{24}{3}<\frac{3y}{3}\le\frac{48}{3}

    8<y168<y\le 16

  4. Keep track of which endpoint is included. The left relation stayed strict (<<) and the right stayed non-strict (\le), so y=16y=16 is a solution but y=8y=8 is not.

  5. Verify with one interior value and both endpoints. At y=10y=10: 3(10)8=223(10)-8=22 and 16<224016<22\le40 holds. At y=16y=16: 3(16)8=403(16)-8=40 and 404040\le40 holds. At y=8y=8: 3(8)8=163(8)-8=16 and 16<1616<16 is false — exactly as the open endpoint predicts.

  6. Write the solution set in interval notation.

    y(8,16]y\in(8,\,16]

Answer

8<y16ory(8,16]8 < y \le 16 \quad\text{or}\quad y \in (8,\,16]

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