Ratios & Proportions
Unit rate route
Compute what one unit costs first, then scale. Slower, but it keeps units visible and catches inverted setups.
The Formula
Unit Rate = b / a; Answer = Unit Rate x c
Compute what one unit costs first, then scale. Slower, but it keeps units visible and catches inverted setups.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| b / a | Value per single unit | per unit | 2.3333 means each unit costs 2.3333 whatever the currency. |
| c | Target quantity | number | The number of units you actually want. |
What Each Symbol Means
b / aper unit
Value per single unit
2.3333 means each unit costs 2.3333 whatever the currency.
cnumber
Target quantity
The number of units you actually want.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to solve a proportion page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Solve A Proportion, filed under Math. Every number the guide produces comes from substituting into this one line.