How do we write 10 & 9 in roman numerals?

Think of breaking down 1999 as 1000+900+90+9 ?

Think 999 as 500 + 400 + 90 + 9

Remember the questions we did till now.

What is the roman numeral for 100?

How can you write 100 in roman numeral.

Think 691 as 500 + 100 + 90 + 1

Think 4999 as 1000 + 1000 + 1000 + 1000 + 999

In roman numerals, What happens when we have a smaller number before a bigger number?