Percent of a Quantity - Pre Algebra

1. What is $0.5\%$ of 400?

   $2$. $0.5\% = 0.005$, and $0.005 \times 400 = 2$.

2. What is a quick mental way to find $10\%$ of a number?

   Divide the number by 10, which moves the decimal point one place to the left. For example, $10\%$ of 47 is 4.7.

3. A test has 40 questions. A student answers $85\%$ of them correctly. How many questions did the student answer correctly?

   34. $0.85 \times 40 = 34$.

4. What decimal do you multiply by to find $35\%$ of a number?

   $0.35$. A percent means per hundred, so $35\% = \frac{35}{100} = 0.35$.

5. 12 is $30\%$ of what number?

   $40$. Solve $0.3w = 12$: $w = 12 \div 0.3 = 40$.

6. Which equation matches the statement that $p\%$ of a whole $W$ is the part $P$?

   $P = \frac{p}{100} \times W$. The percent, written as a decimal or fraction, acts as a multiplier on the whole.

7. Use the fact that $a\%$ of $b$ equals $b\%$ of $a$. What is $8\%$ of 50?

   $4$. $8\%$ of 50 equals $50\%$ of 8, which is 4.

8. What is $120\%$ of 50?

   $60$. $1.2 \times 50 = 60$; a percent above $100\%$ gives more than the original quantity.

9. In a class of 30 students, $60\%$ are girls and the rest are boys. How many boys are in the class?

   12. The boys are $40\%$ of the class, and $0.4 \times 30 = 12$.

10. What is $25\%$ of 64?

    $16$. $25\% = \frac{1}{4}$, and $\frac{1}{4}$ of 64 is 16.

11. A meal costs 40 dollars, and the tip is $18\%$ of the meal cost. How much is the tip?

    7.20 dollars. $0.18 \times 40 = 7.2$.

12. What is $15\%$ of 80?

    $12$. $0.15 \times 80 = 12$.

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