How do you write $8\dfrac{21}{25}$ as a decimal?

Hint: We will look at the definition of a mixed fraction. We will see the steps to convert a mixed fraction into a decimal number. These steps involve the division operation and the addition operation. We will look at an example and execute these steps. Then we will convert the given mixed fraction into a decimal number using the same steps.

Complete step by step answer:
A mixed fraction is defined as a combination of a whole number and a proper fraction. An example of a mixed fraction is $1\dfrac{1}{2}$. This mixed fraction in words is 'one and a half'.
We can convert a mixed fraction into its decimal form. The steps for doing this are as follows,
(i) We will divide the numerator by the denominator and obtain the decimal for the proper fraction part.
(ii) We will add this decimal number to the whole number part of the mixed fraction.
So, if the mixed fraction is $1\dfrac{1}{2}$, then after step (i) we get the decimal form of the proper fraction part as 0.5. Now, according to step (ii), we will add this decimal form to the whole number and get $1+0.5=1.5$. Therefore, the decimal form of the mixed fraction $1\dfrac{1}{2}$ is 1.5.
Now, the given mixed fraction is $8\dfrac{21}{25}$. According to step (i), we will convert the proper fraction part into a decimal number. Dividing 21 by 25, we get $\dfrac{21}{25}=0.84$. Next, according to step (ii), we will add this decimal number to the whole number in the mixed fraction. So, we have $8+0.84=8.84$.
Therefore, the decimal form of the given mixed fraction is 8.84.

Note:
We should be familiar with the concept of a fraction and its types. There are proper fractions, improper fractions and mixed fractions. We use a fraction to express how many parts of a certain size are there. There are equivalent fractions of a given fraction. These are obtained by multiplying the same number in the numerator and the denominator.