Solve for an Unknown Fraction
Find the missing number in a proportion a/b = c/d.
Change the values and press Calculate to work out your own figures.
Enter three of the four numbers and leave the unknown empty.
Show the working
- Cross-multiply: a × d = b × c
- Solve for the blank: 4.5
How to use it
Enter three of the four numbers and leave the unknown empty.
Numbers can be whole numbers, decimals (0.75), fractions (3/4), mixed numbers (1 1/2), repeating decimals (0.(3)) and, where a percent is asked for, percentages (75%). Show the working gives each step.
Key facts
a/b = c/d ⇔ ad = bc
Cross-multiplying
Multiply diagonally and solve the one-step equation for the unknown.
Questions
If 3/x = 2/3, what is x?
4.5.
If x/8 = 3/4?
6.
Formulas
a/b = c/d ⇔ ad = bc
Sources
Limitations
- Numbers have at most 120 digits.