How many years is a decade, a century?

Hint: As we know that, in order to define time we have named several period of time as particular name such as smallest standard unit of time is a second and then \[60\sec \] named as one minute and later on several period of time as an hour which is composed of $60\min $ $24\,hours$ is termed as a day. We will learn basic names given to periods of time and then will figure out the relation between a decade and a century.

Complete step by step answer:
Since, we know a week is named after $7\,days$ then $4\,weeks$ constitute a month then $12months$ are said to be a year. Since, the measurements of periods of time can be very large and we can actually calculate the number of days or the number of years in order to define it.

Since, the periods of time can be very large so we named new words such as a decade and century.A decade is named for ten years or the ten years are collectively known as a decade.
$1\,decade = 10\,years$
Similarly, a century is named for hundred years or the hundred years collectively known as a century.
$1\,century = 100\,years$
So, we can see that from the definition of a decade and century
$1\,century = 10\,decades.$

Hence, ten years is a decade and hundred years is a century and both are related as $1\,century = 10\,decades.$

Note: It should be remembered that, the periods of time which are mentioned here are all with respect to our earth time observation such as $24\,hours$ makes a day, so it is not necessary that this will be true for all planets, the basic period of time for different planets is mainly depends upon how long it takes to complete its revolution around the sun.