Assuming that the weights of 10,000 items are normally distributed and that the distribution has a mean of 115 kg and a standard deviation of 3 kg: 

(a) Estimate how many items have weights between 115 and 118 kg; 

(b) If you have to pick one item at random from the whole 10,000 items, how confident would you be in predicting that its value would lie between 112 and 115 kg?; 

(c) If a sample of 10 items was drawn from the 10,000 items what would be the standard error of the sample mean? What would be the standard error if the sample consisted of 40 items?