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Missing value

Quickly find the unknown value (direct).

Calculator

Known value (a ≠ 0)
Corresponding to a
New value
Rounding

Results

x10.00
ratio (b / a)2.50
Formula
—

Examples

Click to prefill

Definition & formula

Direct proportion: the ratio b/a is constant.

Formula
—
  1. Calculate the ratio: b / a.
  2. Multiply by c: x = (b/a) × c.
  3. Check that a ≠ 0.
If c doubles, then x doubles (direct proportion).
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Inverse rule of threeSolve an inverse proportionality problem.
Complete a proportionality table.Complete the missing values of a table.
Check if a table is proportional.Test if the rows/columns are proportional.

About: Finding a missing value

This tool automatically calculates the missing value in a proportionality situation from three known values.

Typical cases

  • School exercisesCalculate the fourth proportional.
  • Quick checkVerify a calculation without redrawing the entire table.
  • Concrete applicationsAdjust a price, a recipe, or a duration.

What the tool provides

The calculated missing value.

An immediate solution without an intermediate table.

Points of attention

  • The relationship must be proportional.
  • Do not confuse with an inverse case.

Tip

Before calculating, ask yourself if the sought value should increase or decrease.