Fractional part of a number, part 1
Finding a fractional part of a number is done by translating the word problem into a multiplication equation. The word “of” means multiply, and the word “is” means equals. So “3/4 of 20 is what number?” becomes 3/4 × 20 = n. Multiply to solve: 3/4 × 20 = 60/4 = 15. This approach — translating words to math operations — is the same method used in percent problems and algebraic word problems. This skill is covered in Saxon Math, Course 2, as part of 7th grade fraction operations.
Key Concepts
Property We can solve fractional part of a number problems by translating the question into an equation. To translate, we replace the word is with $=$ and we replace the word of with $\times$.
Examples Three fifths of $120$ is what number? $\rightarrow \frac{3}{5} \times 120 = W N \rightarrow W N = 72$ What number is $\frac{2}{3}$ of $21$? $\rightarrow W N = \frac{2}{3} \times 21 \rightarrow W N = 14$.
Explanation Think of word problems as a secret code where 'is' means equals ($=$) and 'of' means multiply ($\times$). Simply translate the sentence into a math equation to find the unknown number. It’s like being a math detective on a mission to crack a numerical case!
Common Questions
How do you find a fractional part of a number?
Translate ‘of’ to multiplication and ‘is’ to equals, then multiply. For ‘2/3 of 18 is what?’ write 2/3 × 18 = 36/3 = 12.
What does ‘of’ mean in a math word problem?
In fraction and percent word problems, ‘of’ means multiply. So ‘1/4 of 40’ means 1/4 × 40 = 10.
How is finding a fractional part of a number different from finding a fraction of a group?
They’re essentially the same operation. ‘Finding a fractional part’ tends to mean applying a fraction to a single number (like finding 3/5 of 25 = 15), while ‘fraction of a group’ applies to a set of objects. Both use multiplication.
What is 3/8 of 40?
3/8 × 40 = 120/8 = 15.
How does this relate to percent problems?
Percent problems use the same translation rule. ‘20% of 50’ becomes 0.20 × 50 = 10. The ‘of’ = multiply rule works for both fractions and percents.
When do students learn fractional parts of a number?
Fractional parts of a number are covered in 7th grade math as part of rational number operations.
Which textbook covers fractional parts of a number?
Saxon Math, Course 2 covers fractional parts of a number.