Ratio & Proportion Calculator (Solve for x)
Use this free ratio and proportion calculator to solve a proportion. Fill in three of the four numbers in a/b = c/d, leave the unknown blank, and the calculator finds it by cross-multiplication — and shows the simplified ratio and the steps.
How to use it
- Enter three of the four values in the proportion a/b = c/d.
- Leave the unknown box blank (or type ?).
- Press Solve to find it and see the cross-multiplication.
Cross-multiplication
If a/b = c/d, then a·d = b·c. The calculator rearranges this to solve for whichever value you left blank.
Original price was: $109.99.$54.99Current price is: $54.99.
Frequently asked questions
How do you solve a proportion?
Cross-multiply (a·d = b·c) and solve for the unknown. The calculator does this and shows the work.
What is a proportion?
A statement that two ratios are equal, such as 2/3 = 4/6.
Original price was: $109.99.$54.99Current price is: $54.99.
Does it simplify the ratio?
Yes — it reduces the ratio to lowest terms and shows the unit rate.
Original price was: $109.99.$54.99Current price is: $54.99.
Read the full lesson: learn the method step by step.
Original price was: $27.99.$17.99Current price is: $17.99.
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