Digits in the tens place are ten times the value of digits in the ones place. 

$\displaystyle 5\times10=50$

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

So, in the problem

$\displaystyle \frac{1}{3}$ of $\displaystyle 45$

We can write it like this

$\displaystyle \frac{1}{3} \cdot 45$

Now, we must write 45 as a fraction.  We know that whole numbers can be written as fractions over 1.  So, we get

$\displaystyle \frac{1}{3} \cdot \frac{45}{1}$

Now, we multiply straight across.  We get

$\displaystyle \frac{1 \cdot 45}{3 \cdot 1}$

$\displaystyle \frac{45}{3}$

$\displaystyle 15$

Therefore, $\displaystyle \frac{1}{3}$ of $\displaystyle 45$ is $\displaystyle 15$.

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

So, in the problem

a quarter of 68

we will first write a quarter as a fraction.  We know a quarter is the same thing as $\displaystyle \frac{1}{4}$.  

So, we can write

$\displaystyle \frac{1}{4}$ of $\displaystyle 68$

Now, we can re-write it like this

$\displaystyle \frac{1}{4} \cdot 68$

Now, we must write 68 as a fraction.  We know that whole numbers can be written as fractions over 1.  So, we get

$\displaystyle \frac{1}{4} \cdot \frac{68}{1}$

Now, we multiply straight across.  We get

$\displaystyle \frac{1 \cdot 68}{4 \cdot 1}$

$\displaystyle \frac{68}{4}$

$\displaystyle 17$

Therefore, $\displaystyle \frac{1}{4}$ of $\displaystyle 68$ is $\displaystyle 17$.

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

$\displaystyle \frac{1}{3} \cdot 39$

$\displaystyle \frac{1}{3} \cdot \frac{39}{1}$

$\displaystyle \frac{1 \cdot 39}{3 \cdot 1}$

$\displaystyle \frac{39}{3}$

$\displaystyle 13$

Therefore,  $\displaystyle \frac{1}{3}$ of $\displaystyle 39$ is $\displaystyle 13$.

The two lines above are the same length. The top line is split into $\displaystyle 4$ pieces and the bottom line is split into $\displaystyle 12$ pieces.

 $\displaystyle \frac{1}{4}$ and $\displaystyle \frac{3}{12}$ are equivalent because they occupy the same position on the number line. 

There is a $\displaystyle 5$ in the tens place which means there are five tens in the number $\displaystyle 53.$

There is a $\displaystyle 5$ in the hundreds place which means there are five hundreds in the number $\displaystyle 561$.

When we round a number to the tens place we look to our ones place to tell us if we round up or down. If the number in our ones place is $\displaystyle 5$ or greater, we round up. If the number in the ones place is $\displaystyle 4$ or less, we round down. When we round up, the number in the tens place increases by $\displaystyle 1$. The numbers to the right of the tens place become $\displaystyle 0$ and the numbers to the left of the tens place stay the same. When we round down, the number in the tens place stays the same. The numbers to the right of the tens place become $\displaystyle 0$ and the numbers to the left of the tens place stay the same.

In this case, $\displaystyle 5$ is equal to $\displaystyle 5$ so our rounded number is $\displaystyle 570.$

The circle is split up into $\displaystyle 4$ equal parts. $\displaystyle 1$ of the parts is shaded green, which means $\displaystyle \frac{1}{4}$ of the circle is green. 

$\displaystyle .73=.73$ because the numbers are the same.