Since the mass of an electron is about 1/1837th the mass of a proton, then it will take many, many electrons to equal the *mass* of the helium nucleus. Since the mass of of the helium nucleus is approx. 4.00 amu, then ...
4 amu x 1837 electrons /1 amu = 7348 electrons
You would need about 7350 electrons to equal the mass of a helium nucleus.
This is how to get the answer I just dont understand why the mass of an electron is 1/1837th the mass of a proton when in my book it says. and its 7000 because Its rounded to 1 sig fig