Weegy: The answer is 3...Here's how it works: if we're talking about numbers without decimal places, the last number from left to right that's not zero is the last significant digit. [ Let's count here: 4 (1 digit) 0 (2 digits) 5 (3 digits), and the rest of the zeros don't count.
Ex 500- 1 significant digit
40000001- 8 significant digits.
] (More)

Weegy: C. electron User: The sum of the protons and neutrons in an atom equals the _____.
A.
atomic number
B.
nucleus number
C.
mass number
D.
atomic mass
Weegy: The sum of the protons and neutrons in an atom equals the MASS NUMBER. (More)