Linear Equations and Inequalities: Question 4

Syllabus C2.5, E2.5, C2.6, E2.6

Structured Core 3 marks

(a) Solve the inequality 175x<217 - 5x < 2, showing your working. [2]

(b) nn is an integer that satisfies the inequality in part (a). Write down the smallest possible value of nn. [1]

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Worked solution

Part (a): solving the inequality

Start with

175x<2.17 - 5x < 2.

Step 1: Subtract 1717 from both sides.

5x<217-5x < 2 - 17

5x<15-5x < -15

Step 2: Divide both sides by 5-5.

Dividing (or multiplying) an inequality by a negative number reverses the inequality sign:

x>155x > \frac{-15}{-5}

x>3x > 3

x>3\boxed{x > 3}

Check (with a test value): try x=4x = 4: 175(4)=1720=317 - 5(4) = 17 - 20 = -3, and 3<2-3 < 2 is true. ✓ Try the boundary x=3x = 3: 175(3)=217 - 5(3) = 2, and 2<22 < 2 is false, so x=3x = 3 is correctly excluded. ✓


Part (b): the smallest integer nn

Since x>3x > 3 is a strict inequality, x=3x = 3 is not included, so the solution set is every number greater than 33.

The smallest integer greater than 33 is

n=4\boxed{n = 4}


Final answers

  • (a) x>3x > 3
  • (b) n=4n = 4