A manufacturer produces airmail envelopes whose weight is normally distributed with a mean 1.95 gm and standard deviation 0.05 gm. The envelopes are sold in lots of 1000. How many (50 envelopes in a lot will heavier than 2 gm ? (B) (A) 153 156 (C) 155 (D) 150 fallawina ic a nrobability density function