a decade is a period of ten years, while a century is a period of 100 years.
4.5 decades equals 4.5 decades!
No, you don't need a hyphen. It would be 10 decades or ten decades.
100 decades in a millennium
There are 3.5 decades in 35 years
30 decades
There are 10.6 decades. Or 10 decades plus 6 years.
16.7 decades
There are 20 decades.
70 decades
fifty decades
1.2 decades
There are 70 decades in 7 centuries. This is because each century consists of 10 decades, so when you multiply 7 centuries by 10 decades, you get a total of 70 decades.