Equations with percentages - pre-algebra lesson
A lesson for pre-algebra or algebra students on how to set up an equation for a percentage word problem.
First, I review how to write "20% of $29" and "7% of x" as mathematical expressions. In a nutshell, the word "of" translates into multiplication. So, 7% of x simply becomes 0.07x.
Then we are ready to solve two word problems. In the first, Mark pays 23% of their salary (s) in taxes. If he pays $425.50 in taxes, find his salary.
It is easy to write a SIMPLE equation to match this percent problem and then solve it.
The second problem has to do with percentage increase. We know the increase (5%) and the final quantity, and are asked the quantity before the increase. Once again, using the decimal 0.05 for the percentage, and multiplication, allows us to write a simple equation and solve it.
See also
Simple one-step equations with decimals — video lesson
Simple equations with fractions — video lesson
Math Mammoth Rational Numbers — a short workbook where you can find worksheets to match this lesson.
Math Mammoth Grade 7 curriculum (pre-algebra)
Back to rational numbers videos index
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