Fractions Solve for Unknown X
Solve for an unknown value x with this fractions calculator. Find the missing fraction variable in the proportion using cross multiplication to calculate the unknown variable x. Solve the proportion between 2 fractions and calculate the missing fraction variable in equalities or inequalities
Enter 3 values and 1 unknown. For example, enter x/45 = 1/15. The proportion calculator solves for x.
How to Solve for x in Fractions
Solve for x by cross multiplying and simplifying the equation to find x.
Example: Given the equation 4/10 = x/15 solve for x.
- Cross multiply the fractions
4 * 15 = 10 * x
- Solve the equation for x
x = (4 * 15) / 10
- Simplify for x
x = 6
To check the work put the result, 6 back into the original equation
4/10 = 6/15
Cross multiply the fractions and you get
4 * 15 = 6 * 10
60 = 60
Since 60 = 60 is true, you can be sure that x = 6 is the correct answer.
Why Does the Cross Multiplication Calculator for Fractions Work?
Cross multiplying works because you're just multiplying both sides of the equation by 1. Since multiplying anything by 1 doesn't change its value you'll have an equivalent equation.
For example, look at this equation:
If you multiply both sides by 1 using the denominators from the other side of the equation you get:
Note that this doesn't change anything, because multiplying anything by 1 doesn't change its value. So now you have:
Since the denominators are also the same here, b × d, you can remove them and say that:
Which is the result of cross multiplying the original equation:
Cross Multiply from Math Is Fun at http://www.mathsisfun.com/
Cross-Multiplication from Ask Dr. Math at http://mathforum.org/
Cross Products from Ask Dr. Math at http://mathforum.org/
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