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Fractions Solve for Unknown X

Solve for X Fraction Calculator
Answer:
x = 15


Solution by Cross Multiplication

For the equation
\[ \frac{5}{8} = \frac{ x}{ 24} \] The cross product is
\[ 5 \times 24 = 8 \times x \] Solving for x
\[ x = \frac{5 \times 24}{8} \] and reducing
\[ x = 15 \]
Solution by Proportion

Since the equation is an equality

If
24 ÷ 8 = 3

Then it is true that
x ÷ 5 = 3

Solving for x
x = 5 × 3
x = 15

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Calculator Use

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.

  1. Cross multiply the fractions
    4 * 15 = 10 * x
  2. Solve the equation for x
    x = (4 * 15) / 10
  3. 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:

\( \dfrac{a}{b} = \dfrac{c}{d} \)

If you multiply both sides by 1 using the denominators from the other side of the equation you get:

\( \dfrac{a}{b} \times \dfrac{d}{d} = \dfrac{c}{d} \times \dfrac{b}{b} \)

Note that this doesn't change anything, because multiplying anything by 1 doesn't change its value. So now you have:

\( \dfrac{a \times d}{b \times d} = \dfrac{b \times c}{b \times d} \)

Since the denominators are also the same here, b × d, you can remove them and say that:

\( a \times d = b \times c \)

Which is the result of cross multiplying the original equation:

\( \dfrac{a}{b} = \dfrac{c}{d} \)

References

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/



 

Cite this content, page or calculator as:

Furey, Edward "Fractions Solve for Unknown X"; from https://www.calculatorsoup.com - Online Calculator Resource.

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