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Ratio & Proportion Calculator

Solve a proportion A/B = C/D for the missing fourth value using cross-multiplication.

Solve Proportion: A / B = C / D (Find D)
Calculated Value D
20.0000
Formula: D = (B Γ— C) / A
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Calculation Guide & Reference

Ratio & Proportion Mathematics

Ratio and proportion calculator solves A/B = C/D for the missing value using cross-multiplication.

Standardized Mathematical Formula
D = (B Γ— C) / A

A proportion states that two ratios are equal: A/B = C/D. Cross-multiplying (A Γ— D = B Γ— C) and solving for the unknown value gives the missing term.

Variables:
A, B, C:Known values in the proportion
D:The unknown value being solved for
How It Works (Step-by-Step)
  • 1Enter the three known values in the proportion A/B = C/D.
  • 2View the calculated value of D.
Real-World Numerical Example
Solving 3/5 = 12/D

Find the value of D so that 3/5 equals 12/D.

β€’Cross-multiply: D = (B Γ— C) / A = (5 Γ— 12) / 3.
β€’D = 60 / 3 = 20.
Result: D = 20, so 3/5 = 12/20.
Calculation Best Practices & Tips
Examine the discriminant (bΒ² - 4ac) before solving quadratics to instantly know if roots are real, distinct, repeated, or complex.
In statistical analysis, always check both the mean and median to identify if data distribution is skewed by outliers.
When calculating percentage changes, ensure you divide by the original starting baseline value: ((New - Old) / Old) * 100.

Frequently Asked Questions (FAQ)

In a proportion A/B = C/D, cross-multiplication means A Γ— D = B Γ— C. This turns the proportion into a simple equation you can solve for any single unknown value.

A ratio (like 3:5) compares two quantities. A proportion is an equation stating that two ratios are equal (like 3/5 = 12/20) β€” a proportion always involves two ratios, a ratio is just one.

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