The net weight is 330 g. The weight of one staple is 0.330g or 330mg.
Work Step by Step
Subtract the weight of the packaging to find the net weight of the 1000 staples. $350g-20g=330g$ Divide by the number of envelopes to find the weight per envelope. $330g\div1000=0.330g$ Move the decimal to convert g to mg. $0.330g=330 mg$