Direct Proportion: The Constant Ratio
Explore how y = kx represents a constant ratio between two quantities.
Equation
y = 2*x
Graph
Table
| x | y |
|---|---|
| 1 | 2 |
| 2 | 4 |
| 3 | 6 |
| 4 | 8 |
| 5 | 10 |
What this lesson covers
What you do
You shape the function y = k*x and watch the graph answer.
Challenges to clear
- Make the line pass through (3, 12). What is the constant ratio k = y/x?
- The ratio never changes: the same k must put (5, 20) on the line too.
- This ratio is not a whole number. The bottom of it is 4 — slide m there.
- Now the top: 8 units must give 6. The constant ratio y ÷ x is 3/4, and it stays 3/4 at every single row.
Check yourself
In a direct proportion y = kx, what does the value of k represent?
If 4 kg of apples cost Rs 80, what is the constant of proportionality k?
- The fixed ratio y/x for any pair of values. — correct
- The value of y when x is 0.
- The sum of x and y.
- The difference between y and x.
- 20 — correct
- 80
- 4
- 320
Think about it
- If k is the ratio y/x, what happens to the ratio if you double k?