Protons = Atomic number
Protons + Neutrons = Mass Number
Protons = 20
Neutrons = Atomic number - Mass number
Neutrons = 82 - 20 = 62
Answer: 0.4
Explanation: The easiest way to do this is to get a denominator of 10. To do this, multiply each number in 2/5 by 2. You will get the fraction 4/10. With the denominator of 10, the answer would be 0.4 by putting the decimal in front of the number.