Math Help - normal distribution help

1. normal distribution help

I'm studying for my final tomorrow..I missed a few classes though so I'm trying to teach myself most of what I'm going over right now..I got a hand out of some review problems...They have the answers but doesn't show how to do the work..here's what I'm stuck on at the moment:

Suppose that the weights of adult males are normally distributed with a mean of 180 pounds and a standard deviation of 20 pounds.

(a) What percent of males weigh less than 170 pounds

(b) If we take a sample of 16 men chosen randomly, what is the probability that their average weight will be less than 170 pounds.

(c) For the sample of 16 men, what proportion of the 16 men would be expected to weigh less than 170 pounds? Answer is .3085

(d) For the sample of 16 men, what is the probability that their total weight would be less than 2720 pounds? (Hint: how does the total weight relate to the average weight.) Answer is .0228

I'm stuck on C and D..is there a way I'm supposed to set these up or are these questions just critical thinking questions where the other 2 answers are the answers for these 2 questions?

2. Originally Posted by mikeyrocks
I'm studying for my final tomorrow..I missed a few classes though so I'm trying to teach myself most of what I'm going over right now..I got a hand out of some review problems...They have the answers but doesn't show how to do the work..here's what I'm stuck on at the moment:

Suppose that the weights of adult males are normally distributed with a mean of 180 pounds and a standard deviation of 20 pounds.

(a) What percent of males weigh less than 170 pounds

(b) If we take a sample of 16 men chosen randomly, what is the probability that their average weight will be less than 170 pounds.