APEMAN

A= Atomic number

P= Protons

E= Electrons

M= Mass number

-Atomic number=

Neutrons

A= Atomic number

P= Protons

E= Electrons

M= Mass number

-Atomic number=

Neutrons

M stands for Mass number

to find the mass number, take the atomic number and round it to the nearest whole number.

Mass number- Atomic number = Neutrons

(M-A=N)

So... 27-13= 14 neutrons!

There are ways to check if your answer makes sense:

Your answers will always be whole numbers

protons and electrons will always be the same number

neutrons for the first 20 elements will be close to or the same as the atomic number