5/8 = x/40 — What Is X?
In the proportion 5/8 = x/40, the missing value is x = 25.
How to use this tool
- Enter A and B (the known fraction).
- Enter C (the denominator of the unknown fraction).
- Read X, the missing numerator.
Cross-multiply and solve: enter three values of a proportion to find the fourth.
Frequently asked questions
- How do I solve a proportion?
- Cross-multiply: A/B = X/C means A × C = B × X, so X = (A × C) / B. Example: 3/4 = X/12 → X = (3 × 12) / 4 = 9.
- What is a proportion used for?
- Proportions are used in scaling recipes, map distances, currency conversions, mixing solutions, and calculating probabilities.