Formula
Cross-multiplication isolates the missing value:
X = B × C / A
The ratio page reduces a finished pair. This page finds the fourth number.
Assumptions
- A is not zero.
- The two ratios are equal.
Worked example
If 2 / 4 = 3 / X, then X is 6.
Input definitions
- A and B
- The known ratio.
- C
- The numerator of the second ratio.
Limitations
Results are rounded for display. This is a classroom calculation, not a measurement from a lab or a financial filing.
Questions
Which number is solved?
The denominator of the second ratio.
What if A is zero?
The proportion cannot be solved, so the form asks for another A.