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Cross Multiply Calculator

A B = C D

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Use this Cross Multiply Calculator to quickly find the value of an unknown variable in a proportion. This tool makes fraction multiplication fast, accurate, and easy. If you want to learn the step-by-step method behind it, keep reading!

How Does Cross Multiplication Work?

In mathematics, cross multiplication involves:

Multiplying the numerator of the first fraction by the denominator of the second fraction
Multiplying the denominator of the first fraction by the numerator of the second fraction

Our free calculator follows this method to solve proportions accurately. You can also use a fraction calculator to add, subtract, multiply, or divide fractions.

Cross Multiplication Formula

For a proportion:

$$ \frac{A}{B} = \frac{C}{D} $$

The cross multiplication rule is:

$$ A \times D = B \times C $$

Step-by-Step Examples

Example 1:

Find B if:

$$ \frac{4}{B} = \frac{7}{9} $$

Solution:

Cross multiply:

$$ 4 \times 9 = B \times 7 $$

$$ B = \frac{36}{7} $$

$$ B \approx 5.14 $$

Example 2:

Find C if:

$$ \frac{1}{6} = \frac{C}{2} $$

Solution:

Cross multiply:

$$ 1 \times 2 = 6 \times C $$

$$ C = \frac{2}{6} = \frac{1}{3} $$

How the Cross Multiply Calculator Works

Input:

Enter any three known values in the four fields
Leave the unknown value blank
Click the Calculate button

Output:

Displays the value of the unknown variable
Solves the proportion accurately using cross multiplication

FAQs

Why does cross multiplication work?

Cross multiplication works because it converts two fractions into equivalent products, eliminating the need to find common denominators.

Who invented cross multiplication?

Cross multiplication does not have a single inventor. It has been used since ancient times as a standard method for ratios, proportions, and algebra.

Is cross multiplication part of the unitary method?

Yes, it is commonly used in the unitary method to solve ratio and proportion problems efficiently.

Can you cross multiply and divide fractions?

Yes. Cross multiplication multiplies the numerator of one fraction by the denominator of the other to find unknowns in proportions. Using this calculator makes such calculations instant and error-free.

Conclusion

Cross multiplication is a simple yet powerful technique for solving proportions and fraction problems. This calculator provides fast, accurate results and demonstrates the method clearly, making it easy for students and professionals alike.

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