Percent of a number using decimals - handy trick! (6th grade math lesson)
To find a percent of a number, simply write your percentage as a decimal, and use MULTIPLICATION. It's that simple! For example, 23% of 54 becomes 0.23 × 54 which is easy to put to a calculator.
In this lesson we practice this concept both ways, including "translating" multiplications into "percent of a quantity" sentences. I use a calculator when necessary, but sometimes mental math is sufficient.
See also
Percent of number with mental math — video lesson
Math Mammoth Grade 7 curriculum (pre-algebra)