CSEC MATHEMATICS · MODULE 2 · LESSON B6

Simultaneous Equations: Linear and Linear–Quadratic

Solving two linear equations by elimination and substitution, forming them from word problems, and solving a linear equation together with a quadratic.

Intermediate Secondary Level MathematicsM2 2.3M2 2.6M2 2.7≈ 40 min🎮 3 games
Before you start

By the end of this lesson you can…

Step 1 · Watch

Explainer video

5 narrated scenes. Press play, listen and read along — the points appear as they are explained. Use ‹ Prev / Next › or the scene bar to jump to any scene.

LESSON B6 · EXPLAINER

Simultaneous Equations: Linear and Linear–Quadratic

Two unknowns, two clues. Pens and books, adult and child tickets, two lines crossing — simultaneous equations find the one answer that fits both clues.

Narration uses your device’s built-in voice. No sound? Switch to “Captions only” — the captions advance on their own.

Explore in 3D

Simultaneous equations

The solution is where two lines cross.

Step 2 · Read

Key notes

Copy these into your notebook in your own words — that is how they stick.

Elimination

Make the coefficients of one letter equal in size; add if opposite signs, subtract if same signs.

Substitution

Rearrange one equation to y = … or x = …, substitute into the other.

Check

Substitute the solution into BOTH original equations.

Graphical meaning

The solution is the intersection of the two lines.

Word problems

Define both letters, write two equations, solve, answer in words with units.

Linear + quadratic

Substitute the linear equation into the quadratic → solve a quadratic → find both pairs.

Number of solutions

Linear–linear: one (or none/infinitely many for parallel/same lines). Linear–quadratic: 0, 1 or 2 pairs.

Pairs

Always write each solution as an (x, y) pair so x and y stay together.

EXAM TIPS & COMMON MISTAKES

  • Label your equations (1) and (2) and say what you are doing: “(1) × 3”. It earns method marks.
  • Check in the equation you did NOT use to find the second letter.
  • For linear–quadratic, give BOTH solution pairs — one pair loses accuracy marks.
  • When subtracting equations be careful with signs: − (−6y) becomes + 6y.
Play & practise

Games

3 quick games on this lesson. Earn XP and badges as you play — your best score for each game is saved. Games are for practice and do not change your exam readiness. More games in the Mathematics Arcade.

Step 3 · Practise

Paper 1 practice — multiple choice

8 items modelled on real CSEC Paper 1 questions. Choose one answer for each, then check. Aim for 80% or better. Work each item on paper first.

CSEC Paper 01 style · SO 2.3

1. If x + y = 7 and x − y = 1, then x is

Answer: B. Add: 2x = 8 → x = 4.
CSEC Paper 01 style · SO 2.3

2. If 2x + y = 7 and x − y = 2, then y is

Answer: B. Add: 3x = 9, x = 3; then 3 − y = 2 → y = 1.
CSEC Paper 01 style · SO 2.3

3. The solution of 3x + 2y = 12 and 5x − 3y = 1 is

Answer: C. 3(2) + 2(3) = 12 and 5(2) − 3(3) = 1.
CSEC Paper 01 style · SO 2.6

4. 3 pens and 2 books cost $19; a pen and a book together cost $8. The price of a pen is

Answer: D. 3p + 2b = 19, p + b = 8 → p = 3.
CSEC Paper 01 style · SO 2.6

5. The sum of two numbers is 20 and their difference is 6. The larger number is

Answer: C. x + y = 20, x − y = 6 → 2x = 26 → x = 13.
CSEC Paper 01 style · SO 2.3

6. If y = 2x − 1 and 3x + 2y = 12, then x is

Answer: B. 3x + 4x − 2 = 12 → 7x = 14 → x = 2.
CSEC Paper 01 style · SO 2.7

7. The line y = x + 2 meets the curve y = x² at the points

Answer: A. x² = x + 2 → (x − 2)(x + 1) = 0.
CSEC Paper 01 style · SO 2.7

8. x + y = 5 and xy = 6. The possible values of x are

Answer: B. x(5 − x) = 6 → x² − 5x + 6 = 0 → x = 2 or 3.
Step 4 · Apply

Paper 2 practice — structured questions

Write full answers, then reveal the mark scheme and tick the points you earned (19 marks in total). Show all your working — method marks count. Your answers are saved on this device.

CSEC Paper 02 style · Module 2 (Simultaneous equations)

Question 1 [11 marks]

Answer all parts.

(a) Solve algebraically: 4x + 3y = 17 and 2x − y = 1. [3]

MARK SCHEME — (a) (max 3)

(b) Two adult tickets and three child tickets cost $44. One adult ticket and two child tickets cost $26. Form two equations and find the price of an adult ticket and of a child ticket. [4]

MARK SCHEME — (b) (max 4)

(c) Solve the simultaneous equations y = 2x + 1 and y = x² − 2. [4]

MARK SCHEME — (c) (max 4)

CSEC Paper 02 style · Module 2 (Simultaneous equations in context)

Question 2 [8 marks]

A shop sells notebooks (n dollars each) and pens (p dollars each). 4 notebooks and 3 pens cost $27. 2 notebooks and 5 pens cost $24.

(a) Write two equations in n and p. [2]

MARK SCHEME — (a) (max 2)

(b) Solve the equations to find the price of a notebook and a pen. [4]

MARK SCHEME — (b) (max 4)

(c) Hence find the cost of 3 notebooks and 2 pens. [2]

MARK SCHEME — (c) (max 2)

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Sources

Where this topic appears in CSEC papers

Find these in your own past-paper booklets for extra timed practice. Items above are written in the style of these papers; any adapted from a specific question say so.