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Miscellaneous Examples · Example 11

Q.Solve the system of inequalities: 3x−7<5+x3x - 7 < 5 + x ... (1), 11−5x≤111 - 5x \le 1 ...

(2) and represent the solutions on the number line.
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The system reduces to x<6x < 6 from (1) and x≥2x \ge 2 from (2). The combined solution is 2≤x<62 \le x < 6, which is a half-open interval on the number line.

When you solve a system of inequalities, you're finding all values of xx that satisfy every inequality at the same time. Think of it like a set of filters: each inequality is a condition that xx must pass. The final solution is the overlap — the region where all conditions hold together.

The key idea is to solve each inequality separately, then combine the results on a number line. The number line isn't just a picture; it's the clearest way to see the intersection of intervals.


  1. Solve inequality (1): 3x−7<5+x3x - 7 < 5 + x

    Start by bringing the xx terms together. Subtract xx from both sides:

3x−x−7<5⇒2x−7<53x - x - 7 < 5 \quad \Rightarrow \quad 2x - 7 < 5

Now add 7 to both sides:

2x<122x < 12

Finally, divide by 2 (positive, so the inequality direction stays the same):

x<6x < 6

So the first condition is: all numbers strictly less than 6.

  1. Solve inequality (2): 11−5x≤111 - 5x \le 1

    Subtract 11 from both sides:

−5x≤1−11⇒−5x≤−10-5x \le 1 - 11 \quad \Rightarrow \quad -5x \le -10

Now divide by −5-5. Crucial: when you divide or multiply an inequality by a negative number, the inequality sign reverses direction.

x≥−10−5⇒x≥2x \ge \frac{-10}{-5} \quad \Rightarrow \quad x \ge 2

So the second condition is: all numbers greater than or equal to 2.

Watch out

A very common mistake is forgetting to flip the inequality sign when dividing by a negative number. If you had written x≤2x \le 2 here, the final answer would be completely wrong.

  1. Combine the two conditions

    We need xx that satisfies both:

    • x<6x < 6
    • x≥2x \ge 2

    This is the intersection of the two intervals. On the number line, you start at 2 (including 2, because of the ≤\le sign) and go up to, but not including, 6. …

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