Overview
In direct proportion, increasing x increases y by the same factor. If y = 10 when x = 4, the constant of proportionality is 2.5, and when x = 10, y becomes 25.
Formula
y = kx, where k = y1 ÷ x1. Therefore, y2 = k × x2.
How it works
1
Enter the known pair
x1 and y1 from the first case.
2
Calculate the constant
Divide y1 by x1.
3
Enter x2
Multiply the constant by x2 to get y2.
Worked examples
Example 1: 4 → 10, and 10 → ?
k = 2.5, so y2 = 25.
Example 2: 2 → 7, and 6 → ?
k = 3.5, so y2 = 21.
Frequently asked questions
How do I know the relationship is direct?
It is direct if the quotient y ÷ x is constant for all pairs.
Can the constant be negative?
Yes, if the values have opposite signs, though the calculator generally assumes positive values.
What is the difference between direct and inverse proportion?
In direct proportion both values increase together; in inverse proportion one increases while the other decreases.
This calculator is for educational and informational purposes only and is not a substitute for professional advice.