Free · Arithmetic calculators ➗

Signed Proportion Cross Products and Worked Steps

This workflow excludes zero in all four positions. General zero-numerator ratios can be valid, but they can leave an inverse denominator undetermined; those cases are not offered here.

  • Formula & worked example
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

Example in initial displayed units: A 2, B 3, D 9 gives C 6.

A/B = C/D; AD = BC

Worked example

Enter these known values and leave the other values blank.

A
2
B
3
D
9
Show isolation steps for
A
C
6

Assumptions and limitations

  • This retained workflow requires four nonzero signed values with absolute magnitude below 999,999,999,999,999. Enter three independent values and clear the fourth. Negative ratios are allowed, but zero numerators and denominators are excluded because their inverses can be singular or underdetermined. The step selector chooses which variable is isolated.
  • Clear unknowns before solving backward and select compatible units. Original reference drawings do not scale to entered values. Independently rounded boundary measurements can be incompatible at finite precision.

Common questions

Can I enter zero in this proportion?

This workflow excludes zero in all four positions. General zero-numerator ratios can be valid, but they can leave an inverse denominator undetermined; those cases are not offered here.

How many measurements are needed?

Enter three nonzero values in A/B = C/D. The fourth is computed; choose a variable in the steps control to see its isolation.

References

The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.

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