The weights of bags of ready-to-eat salad are normally distributed with a mean of 290 grams and a standard deviation of 10 grams. what percent of the bags weigh less than 280 grams? a) 13.5% b) 16% c) 34% d) 36.5%

290-10=280

280 is one standard deviation below.
All that are above mean is 50%.
One standard deviation below is 34%.
50%+34%=84%  all of these bags weigh more than 280 g.
So,
100%-84%=16%  should be bags that are less than 280 g.

Answer is b) 16 %.