Solve a proportion A : B = C : ? for the missing value. Enter the three known terms.
Missing Value
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The fourth term.Usage Tip
Scaling a recipe is a proportion: if 2 cups serves 4, then for 6 people solve 2 : 4 = x : 6.
THE MATH
A : B = C : unknown
Cross-multiply: unknown = B × C ÷ A
Cross-multiply: unknown = B × C ÷ A
A proportion states that two ratios are equal. Given three of the four terms, cross-multiplication solves for the missing one.
This is the basis of scaling recipes, maps, and models.
This is the basis of scaling recipes, maps, and models.
Enter A, B, and C; the calculator solves for the fourth term.
A cannot be zero, since the solution divides by A.
Proportions assume the relationship is linear.
A cannot be zero, since the solution divides by A.
Proportions assume the relationship is linear.