# Mathedu

Learn math by practice

# Re-engineering Math

## 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.

For instance, the VAT of 20% multiplies the taxes free amount by 1.2, or else adds 20% of the taxes free amount to itself.

That's why the VAT amount of 20% is NOT 20% of the price, as the price is the taxes included amount. To obtain the VAT amount from the price, you must first DIVIDE the price b...

## The A4 format as a division of a surface of 1 square meter

We all know the A4 format as a rectangle of 21x29.7 cm. But who knows that it is a mathematical construction that implies an A0 format and subsequently A1, A2 and A3?

The basis is the A0 format, a rectangle with a 1 square meter area, with particular proportions. We shall find the ration of the length L0 over width l0 when we construct the A1 format.

The A1 format is half a A0 format. More precisely, its length L1 is the width l0 of the A0 format, and its width l1 is half t...

## Neil Armstrong looses much weight on the moon!

In everyday language, we say that the weight of an object is the number of grams of kilograms itâ€¦ weights!

But the physicians call the number of grams or kilograms the "mass", the weight being the force of gravity induced by the earth mass: P=mg, in Newtons if m is in kilograms and g in meters per seconds to the power 2.

What does that holly mess mean? Are we completely wrong when we speak of the number of kilograms as of the weight?

As a matter of fact, the weight ...