# Add a percentage is a Multiplication

Add a percentage, say 5% is not making an addition. It is a multiplication by (1+5/100). You may also multiply by 5, divide by 100, and then add the result to the original amount.

# Manipulate percentages like a Pro

We learned in the previous post to add a percentage with a multiplication, let’s now learn the different manipulations of percentage.

# Why is there a February 29, 2020, and not in 2021 or 2019?

Well, the day length is exactly the time by which the earth makes a turnaround on itself. And the year is exactly the time by which the earth makes a complete revolution around the sun.
Thus, the number of days of the year must be the ratio of the year length on the day length say, in seconds.
The problem is that there is no reason for that ratio to be an integer…
Our scientific calculators deal sometimes with numbers with a $$E$$ inside: this is the so called Exponential, or Scientific Notation.