MPM2D Linear Systems
Grade 10 Unit 1 — practice questions with full solutions
Solving two equations at once by graphing, substitution and elimination — plus the word problems that always appear on tests.
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- The solution to a system is the point where the lines cross.
- Reading the graph, they intersect at (2, 1).
- Check in y = 2x − 3: 2(2) − 3 = 1. ✔
- Check in y = −x + 3: −(2) + 3 = 1. ✔
- Both are satisfied, so (2, 1) is confirmed.
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- The first equation is already solved for y, so substitute it into the second.
- 2x + (3x − 4) = 11.
- Simplify: 5x − 4 = 11, so 5x = 15 and x = 3.
- Substitute back: y = 3(3) − 4 = 5.
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- The y terms are already opposites, so add the two equations directly.
- (3x + 5x) + (2y − 2y) = 16 + 8 gives 8x = 24.
- So x = 3.
- Substitute into the first: 3(3) + 2y = 16, so 2y = 7 and y = 3.5.
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- Neither variable eliminates yet, so multiply to match coefficients. Multiply the first by 5 and the second by 3.
- 20x + 15y = 50 and 9x + 15y = 39.
- Subtract: 11x = 11, so x = 1.
- Substitute into 4(1) + 3y = 10: 3y = 6, so y = 2.
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- Let a be adult tickets and s student tickets.
- Ticket count: a + s = 250. Revenue: 12a + 7s = 2400.
- From the first, s = 250 − a. Substitute: 12a + 7(250 − a) = 2400.
- Expand: 12a + 1750 − 7a = 2400, so 5a = 650 and a = 130.
- Then s = 120. Check: 12(130) + 7(120) = 1560 + 840 = 2400. ✔
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- Let c be the canoe speed and r the current speed.
- Downstream the speeds add: c + r = 24 ÷ 2 = 12.
- Upstream they subtract: c − r = 24 ÷ 3 = 8.
- Add the two equations: 2c = 20, so c = 10.
- Then r = 12 − 10 = 2.
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- Infinitely many solutions means the two equations describe the same line.
- Compare the x terms: 6 ÷ 2 = 3, so the second equation must be exactly 3 times the first.
- Check the constants: 3 × 7 = 21. ✔ This is consistent.
- So the y term must satisfy k = 3 × 3 = 9.
- Note that if the constant had not matched, no value of k would work — the lines would be parallel instead.
MPM2D Linear Systems — common questions
Short answers to the things students ask most about this unit.
Should I use substitution or elimination?
Use substitution when one equation is already solved for a variable, or easily can be. Use elimination when the equations are both in standard form and coefficients line up.
What does it mean if a system has no solution?
The lines are parallel — same slope, different intercept — so they never cross. If both equations describe the same line, there are infinitely many solutions instead.
The classes teach the method behind every one of these.
The solutions above show the steps. The classes teach how to think about the problem in the first place — interactive, and worked through at the student’s own pace. Try 3 complete classes free — no payment required to begin.
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