How To Calculate An Unknown Total When You Know The Amount Of The Percent

Algebra is a mathematical method used to calculate unknown values. Variables, which are generally represented by a letter of the alphabet, represent unknown values in an equation. Isolating the variable determines its value. Algebra is part of the high school math curriculum but also applies to many real-life situations. For example, calculating the value of a total from a known percentage is a valuable tool for determining the total number of voters in an election or calculating the total salary based on a percentage raise.

1. Understand Percentages

Understand the meaning of percentage. The word percent comes from a Latin word meaning "for each 100." A percentage is essentially a fraction, with a denominator of 100. For example, 2 percent is equal to 2 ÷ 100, or 2 for each 100.

2. Note Percentage Value

Note the value of the percentage. For example, if 2 percent = 80, know that 2 for each 100 is the same as 80 for each of the unknown value.

3. Create Equation

Create an equation that shows the fractional relationship between the percentage and its value. Use the variable x to represent the unknown total. In this case,

\(\frac{2}{100} = \frac{80}{x}\)

4. Cross-multiply Equation

Cross-multiply the equation to bring the variable to one side of the equation as a whole number. Multiply values diagonal from each other in the equation, i.e.,

\(\frac{2}{100} = \frac{80}{x}\)

to create the whole number equation of

\(2x = 8000\)

5. Isolate Variable

Divide both sides of the equation by the coefficient, 2. On the left side:

\(\frac{2x}{2} = x\)

On the right side

\(\frac{8000}{2} = 4000\)

The resulting equation is

\(x = 4000\)

6. Check Work

Check your work by introducing the value of ​x​ into the original equation,

\(\frac{2}{100} = \frac{80}{x}\)

Replace ​x​ with 4000 and solve both sides of the equation to ensure that it balances. Use a calculator or sheet of paper to show that

\(\frac{2}{100}= 0.02 \text{ and } \frac{80}{4000}= 0.02\)