To find a percentage of a whole, we will multiply the percent by the whole number.

So, in the problem

$\displaystyle 20\%$ of $\displaystyle 50$

we can write it as

$\displaystyle 20\% \cdot 50$

Now, to multiply, we need to write $\displaystyle 20\%$ as a fraction.  A percentage can be rewritten as the number over 100.  So, we get

$\displaystyle \frac{20}{100} \cdot 50$

Now, we need to write $\displaystyle 50$ as a fraction.  Any whole number can be written as a fraction by simply writing it over 1.  So, we get

$\displaystyle \frac{20}{100} \cdot \frac{50}{1}$

Before we multiply, we can simplify the fractions to make things easier.  The zero in 20 can cancel a zero in 100.  We get

$\displaystyle \frac{2}{10} \cdot \frac{50}{1}$

The zero in 10 can cancel the zero in 50.  We get

$\displaystyle \frac{2}{1} \cdot \frac{5}{1}$

Now, we can multiply.  To multiply fractions, we will multiply straight across.  We get

$\displaystyle \frac{2 \cdot 5}{1 \cdot 1}$

$\displaystyle \frac{10}{1}$

$\displaystyle 10$

Therefore, $\displaystyle 20\%$ of $\displaystyle 50$ is $\displaystyle 10$.

To find percentage of a whole number, we will multiply the percent by the whole number.  

So, given the problem 

$\displaystyle 10\%$ of $\displaystyle 40$

we can write it as

$\displaystyle 10\% \cdot 40$

To multiply a percentage, we will re-write the percentage as a fraction.  We know that percentages can be written as that number over 100.  So, we get

$\displaystyle \frac{10}{100} \cdot 40$

Now, we will write 40 as a fraction.  We know that whole numbers can be written as that number over 1.  So, we get

$\displaystyle \frac{10}{100} \cdot \frac{40}{1}$

Now, before we multiply, we will simplify to make things easier.  The zero in 10 and a zero in 100 can be cancelled.  We get

$\displaystyle \frac{1}{10} \cdot \frac{40}{1}$

The zero in 10 can be cancelled with the zero in 40.  We get

$\displaystyle \frac{1}{1} \cdot \frac{4}{1}$

Now, we will multiply straight across. 

$\displaystyle \frac{1 \cdot 4}{1 \cdot 1}$

$\displaystyle \frac{4}{1}$

$\displaystyle 4$

Therefore,  $\displaystyle 10\%$ of $\displaystyle 40$ is $\displaystyle 4$.

To find a percentage of a whole number, we will multiply the percentage by the whole number. 

So, in the problem

$\displaystyle 15\%$ of $\displaystyle 30$

we can write it as

$\displaystyle 15\% \cdot 30$

Now, we will write the percentage as a fraction.  To do that, we write the number over 100.  So,

$\displaystyle \frac{15}{100} \cdot 30$

To multiply, we also need to write 30 as a fraction.  To do that, we write the whole number over 1.  So,

$\displaystyle \frac{15}{100} \cdot \frac{30}{1}$

Now, before we multiply, we will simplify to make things easier.  The zero in 100 can cancel the zero in 30.  So,

$\displaystyle \frac{15}{10} \cdot \frac{3}{1}$

Now, we will multiply straight across.  We get

$\displaystyle \frac{15 \cdot 3}{10}$

$\displaystyle \frac{45}{10}$

$\displaystyle 4.5$

Therefore, $\displaystyle 15\%$ of $\displaystyle 30$ is $\displaystyle 4.5$.

To find a percentage of a whole number, we will multiply the percentage by the whole number. So, in the problem

$\displaystyle 70\%$ of $\displaystyle 150$

we can write it as

$\displaystyle 70\% \cdot 150$

Now, we will write 70% as a fraction.  We know that a percentage can be written as the number over 100.  So, we get

$\displaystyle \frac{70}{100} \cdot 150$

Now, we will write 150 as a fraction.  To write a whole number as a fraction, we will write the number over 1.  We get

$\displaystyle \frac{70}{100} \cdot \frac{150}{1}$

Now, before we multiply, we can simplify to make things easier.  

The zero in 70 can cancel a zero in 100.  So,

$\displaystyle \frac{7}{10} \cdot \frac{150}{1}$

The zero in 10 can cancel the zero in 150.  So,

$\displaystyle \frac{7}{1} \cdot \frac{15}{1}$

Now, we can multiply straight across. We get

$\displaystyle \frac{7 \cdot 15}{1 \cdot 1}$

$\displaystyle \frac{105}{1}$

$\displaystyle 105$

Therefore, $\displaystyle 70\%$ of $\displaystyle 150$ is $\displaystyle 105$.

To find a percentage of a whole number, we will multiply the percentage by the whole number.

So, 

$\displaystyle 20\%$ of $\displaystyle 80$

can be written as

$\displaystyle 20\% \cdot 80$

Now, we will write 20% as a fraction.  We know that percentages can be written as the number over 100.  So,

$\displaystyle \frac{20}{100} \cdot 80$

Now, we will write 80 as a fraction.  We know that whole numbers can be written as the number over 1.  So,

$\displaystyle \frac{20}{100} \cdot \frac{80}{1}$

Now, we can simplify before multiplying to make things easier.  The zero in 20 can cancel a zero in 100. So,

$\displaystyle \frac{2}{10} \cdot \frac{80}{1}$

The zero in 10 can cancel the zero in 80.  So,

$\displaystyle \frac{2}{1} \cdot \frac{8}{1}$

Now, we can multiply straight across.  We get

$\displaystyle \frac{2 \cdot 8}{1 \cdot 1}$

$\displaystyle \frac{16}{1}$

$\displaystyle 16$

Therefore, $\displaystyle 20\%$ of $\displaystyle 80$ is $\displaystyle 16$.

To find a percentage of a whole number, we will multiply the percentage by the whole number. 

So, in the problem

$\displaystyle 25\%$ of $\displaystyle 500$

we can write it as

$\displaystyle 25\% \cdot 500$

Now, we can write $\displaystyle 25\%$ as a fraction.  We know that percentages can be written as fractions over 100.  So, we get

$\displaystyle \frac{25}{100} \cdot 500$

Now, we will write $\displaystyle 500$ as a fraction.  We know that whole numbers can be written as fractions over 1.  So, we get

$\displaystyle \frac{25}{100} \cdot \frac{500}{1}$

Now, before we multiply, we can simplify to make things easier.  The zeros in 100 can cancel the zeros in 500.  So, we get

$\displaystyle \frac{25}{1} \cdot \frac{5}{1}$

Now, we can multiply straight across.  We get

$\displaystyle \frac{25 \cdot 5}{1 \cdot 1}$

$\displaystyle \frac{125}{1}$

$\displaystyle 125$

Therefore, $\displaystyle 25\%$ of $\displaystyle 500$ is $\displaystyle 125$.

To find a percentage of a whole number, we will multiply the percentage by the whole number.  So, in the problem

$\displaystyle 30\%$ of $\displaystyle 250$

we can re-write it like

$\displaystyle 30\% \cdot 250$

Now, we can multiply.  First, we will write the percentage as a fraction.  We know that percentages can be written as fractions over 100.  So, we get

$\displaystyle \frac{30}{100} \cdot 250$

Now, we will write 250 as a fraction.  We know that whole numbers can be written as fractions over 1.  So, we get

$\displaystyle \frac{30}{100} \cdot \frac{250}{1}$

Now, before we multiply, we will simplify to make things easier. The zero in 30 and the zero in 100 can cancel.  So, we get

$\displaystyle \frac{3}{10} \cdot \frac{250}{1}$

Now, the zero in 10 can cancel the zero in 250.  So, we get

$\displaystyle \frac{3}{1} \cdot \frac{25}{1}$

Now, we can multiply straight across.  We get

$\displaystyle \frac{3 \cdot 25}{1 \cdot 1}$

$\displaystyle \frac{75}{1}$

$\displaystyle 75$

Therefore, $\displaystyle 30\%$ of $\displaystyle 250$  is $\displaystyle 75$.

To find a percentage of a whole number, we will multiply the percentage by the whole number. 

So, given the problem

$\displaystyle 40\%$ of $\displaystyle 80$

we can re-write it as

$\displaystyle 40\% \cdot 80$

Now, to multiply, we will write both numbers as fractions.  So, to write $\displaystyle 40\%$ as a fraction, we know percentages can be written as fractions over 100.  So, we get

$\displaystyle \frac{40}{100} \cdot 80$

Now, to write $\displaystyle 80$ as a fraction, we know whole numbers can be written as fractions over 1.  So, we get

$\displaystyle \frac{40}{100} \cdot \frac{80}{1}$

Now, before we multiply, we will simplify to make things easier.  The zero in $\displaystyle 40$ can cancel a zero in $\displaystyle 100$. So, we get

$\displaystyle \frac{4}{10} \cdot \frac{80}{1}$

Now, the zero in $\displaystyle 10$ can cancel the zero in $\displaystyle 80$.  So, we get

$\displaystyle \frac{4}{1} \cdot \frac{8}{1}$

Now, we can multiply straight across.  We get

$\displaystyle \frac{4 \cdot 8}{1 \cdot 1}$

$\displaystyle \frac{32}{1}$

$\displaystyle 32$

Therefore,  $\displaystyle 40\%$ of $\displaystyle 80$ is $\displaystyle 32$.

To find a percentage of a whole number, we will multiply the percentage by the whole number.  So, in the problem

$\displaystyle 10\%$ of $\displaystyle 90$

we can write 

$\displaystyle 10\% \cdot 90$

Now, we will write $\displaystyle 10\%$ as a fraction.  We know that percentages can be written as fractions over 100.  So, we get

$\displaystyle \frac{10}{100} \cdot 90$

Now, we will write $\displaystyle 90$ as a fraction.  We know that whole numbers can be written as fractions over 1.  So, we get

$\displaystyle \frac{10}{100} \cdot \frac{90}{1}$

Now, before we multiply, we will simplify to make things easier.  The zero in 10 can cancel a zero in 100.  So, we get

$\displaystyle \frac{1}{10} \cdot \frac{90}{1}$

The zero in 10 can cancel the zero in 90.  So, we get

$\displaystyle \frac{1}{1} \cdot \frac{9}{1}$

Now, we can multiply straight across.  We get

$\displaystyle \frac{1 \cdot 9}{1 \cdot 1}$

$\displaystyle \frac{9}{1}$

$\displaystyle 9$

Therefore, $\displaystyle 10\%$ of $\displaystyle 90$ is $\displaystyle 9$.

To find a percentage of a whole number, we will multiply the percentage by the whole number.  So, in the problem

$\displaystyle 45\%$ of $\displaystyle 200$

we can re-write it like this

$\displaystyle 45\% \cdot 200$

Now, to multiply, we will first write $\displaystyle 45\%$ as a fraction.  We know that percentages can be written as fractions over 100.  So, we can write

$\displaystyle \frac{45}{100} \cdot 200$

Now, we will write $\displaystyle 200$ as a fraction.  We know that whole numbers can be written as fractions over 1.  So, we get

$\displaystyle \frac{45}{100} \cdot \frac{200}{1}$

Now, we can simplify before we multiply to make things easier.  The zeros in 100 can cancel the zeros in 200.  So, we get

$\displaystyle \frac{45}{1} \cdot \frac{2}{1}$

Now, we can multiply straight across.  We get

$\displaystyle \frac{45 \cdot 2}{1 \cdot 1}$

$\displaystyle \frac{90}{1}$

$\displaystyle 90$

Therefore,  $\displaystyle 45\%$ of $\displaystyle 200$ is $\displaystyle 90$.