**Understanding time units** *KS3 Revision*

## What you need to know

**Things to remember:**

- It is helpful to think of the time as years first and then convert to other time units.

* *Before we start, it is important to know how long certain periods of time are.

Time Unit Number of Years

1 decade 10

1 century 100

1 millennium 1000

When converting time units into years, we can think of this just like we have when converting measurements.

Time Unit Multiply by Number of Years

1 decade 10 10

1 century 100 100

1 millennium 1000 1000

*What is 7 decades in years?*

* *

7\times10=70

7 decades is the same as 7 years.

*What is 2.27 centuries in years?*

* *

2.27\times100=227

2.27 centuries is the same as 227 years.

*What is 3.2 millennia in years?*

* *

3.2\times1000=3200

3.2 millennia is the same as 3200 years.

But, like with converting units, we can also go the other way by dividing.

Years to Decades Divide by 10

Years to Centuries Divide by 100

Years to Millenia Divide by 1000

*How many decades are there in 75 years?*

* *

75\div10=7.5

There are 7.5 decades in 75 years.

*How many centuries are there in 600 years?*

* *

600\div100=6

There are 6 centuries in 600 years.

*How many millennia are there in 350 years?*

* *

350\div1000=0.35

There are 0.35 decades in 350 years.

## Example Questions

**Question 1:** What is 6.33 centuries in years?

6.33\times100=633

6.33 centuries is the same as 633 years.

**Question 2:** How many millennia are there in 4200 years?

4200\div1000=4.2

There are 4.2 millennia in 4200 years.