Solve Missing Proportion Value
Enter 3 values — leave the unknown field empty
Enter any 3 values — leave the missing value (?) blank
A
B
=
C
D
Examples:
How to Solve Proportions
A proportion states that two ratios are equal: A:B = C:D (or A/B = C/D). To solve for a missing value, use cross multiplication:
A × D = B × C (Cross Products)
Missing D = (B × C) ÷ A
Missing A = (B × C) ÷ D
Missing D = (B × C) ÷ A
Missing A = (B × C) ÷ D
Direct vs Inverse Proportion
Direct proportion (y = kx): As x increases, y increases proportionally. Example: if you drive at constant speed, doubling the time doubles the distance.
Inverse proportion (y = k/x): As x increases, y decreases. Example: more workers on a job → less time needed. The product x×y stays constant.
Real-World Proportion Examples
- Recipe scaling: 2 cups flour for 12 cookies → how much for 30 cookies? → 2:12 = ?:30 → 5 cups
- Map reading: 1cm = 50km on map → 3cm = ? km → 1:50 = 3:? → 150km
- Currency exchange: $1 = ₹83 → $45 = ? → 1:83 = 45:? → ₹3,735
- Speed and time: At 60 km/h takes 4 hours → at 80 km/h takes ? → Inverse: 60×4 = 80×? → 3 hours
Related Calculators
Also check our Ratio Calculator, Fraction Calculator, Percentage Calculator, and all Math Calculators on CalcVelo.