8th Grade algebra · Ages 13–14
Lines and Slope
Every straight line has a rule. Grade 8 learns to read it, draw it, and find where two lines cross.
The one idea
A straight line is a rule: start at b, and for every step right, go up m.
Ready?
8th Grade algebra · Lines and Slope
Every straight line has a rule. Grade 8 learns to read it, draw it, and find where two lines cross.
Full screen — no distractions
For grown-ups: 8th Grade algebra
y = mx + b looks abstract but it is the taxi fare from Grade 7: b is the fee you pay once, m is what each mile adds. When your child is stuck on a graph, ask “where does it start?” and “how much does it go up each step?”.
This page is the right one if they can already…
- Solves two-step equations, including negatives
- Plots coordinates in all four quadrants
- Writes an equation from a story with a fixed fee and a rate
Not yet? Start at 7th Grade: Two Steps Back — algebra only works one rung at a time.
🏠 Try it at home
From table to line
Plot your savings: start with $10, add $5 a week. Where is the line in week 6?
Slope is steepness
Measure a ramp or a slide: height up ÷ length across. Which is steepest in the playground?
Start and step: y = mx + b
Find three costs at home with a fixed part and a per-unit part. Write each as y = mx + b.
Where two lines meet
Gym A: $20 joining + $10 a month. Gym B: $40 joining + $5 a month. When do they cost the same?
The words, in plain English
- Slope (m)
- Rise ÷ run — how steep a line is.
- Slope 2: up 2 for every 1 across.
- y-intercept (b)
- Where the line crosses the y-axis.
- y = 2x + 1 crosses at 1.
- Linear
- Makes a straight line.
- y = 5x + 10
- Function
- A rule giving one output for each input.
- y = 2x + 1
- System of equations
- Two rules that must both be true.
- y = x + 1 and y = −x + 5
🌍 Algebra in an ordinary day
- Comparing two phone plans or gyms — where do the lines cross?
- Ramps and roofs have slopes
- Speed: miles per hour is a slope on a distance-time graph
🏁 By the end of 8th Grade
- Graphs a line from its rule
- Finds slope from two points or a graph
- Writes y = mx + b from a real situation
- Solves a system by finding where two lines meet
Where this fits
One idea, twelve rungs. The hiding spot just gets cleverer.
Frequently Asked Questions
What algebra should a 8th Grade child learn?
A straight line is a rule: start at b, and for every step right, go up m. By the end of the year they should be able to: graphs a line from its rule; finds slope from two points or a graph; writes y = mx + b from a real situation; solves a system by finding where two lines meet.
Isn’t 8th Grade too early for algebra?
No — lines and slope is standard 8th Grade maths in most curricula. This page breaks it into single moves so it never feels like a jump.
What is the most common 8th Grade algebra mistake?
Gets ½ by doing across ÷ up. Two numbers, two ways to divide — and no reason to pick one. The fix: “Rise over run”: you rise out of bed before you run. Up goes on top.
What if my child is stuck?
Go down one rung. Every lesson here builds on the 7th Grade page, and the “ready for this page if” list at the top tells you exactly what they need first. In practice, a wrong answer gives a hint, and a second wrong answer shows the full worked solution.
Is it free?
Yes. All 4 lessons, the pictures, the worked examples, the balance scale and the practice questions are free with no signup. The practice never runs out — every question is generated fresh and checked.