How do you write 20 cents in decimal?

Answer 1

A decimal number is simply a way of representing a number in such a way that the place value of each digit is ten times that of the digit to its right. A decimal representation does not require a decimal point. Adding zeros after the decimal point is wrong because they imply a degree of accuracy (significant figures) for which there is no justification.
So 20 cents, as a decimal, is simply 20 cents.

Answer 2

0.20