Solve for a missing numerator or denominator in a proportion of two fractions using cross-multiplication.
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Enter three values and leave one field empty to solve for the unknown.
Also in Fractions
Fraction Algebra
A solve for unknown fraction calculator finds the missing numerator or denominator in a proportion of two equal fractions using cross-multiplication. Enter three of the four values and the calculator solves for the fourth.
A proportion states that two fractions are equal: a/b = c/d. If one of the four values is unknown, cross-multiplication produces a simple equation that can be solved in one step.
This technique is used in scaling recipes, converting units, solving geometry problems, and any situation where two ratios must remain equal.
Multiply the numerator of each fraction by the denominator of the other. Setting these two products equal gives an equation with one unknown that can be solved by division.
a/b = c/d → a × d = b × c
Cross-multiply to form a linear equation, then isolate the unknown by dividing both sides by its coefficient.
Frequently asked questions
The same cross-multiplication approach works. After cross-multiplying, the unknown appears as a factor on one side and can be isolated by dividing.
Yes. If cross-multiplication does not produce a whole number, the result is left as a simplified fraction, which is a perfectly valid answer.
Yes. A proportion is an equation stating that two fractions or ratios are equal. This calculator solves for the missing term in that equation.
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Solve missing values in a:b = c:d proportions with cross multiplication, then compare the completed ratios and matching products.
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Find equivalent fractions for any given fraction by multiplying or dividing numerator and denominator by the same factor.
Add two or more fractions with like or unlike denominators, find the common denominator automatically, and simplify the result.
