Can I gt some help on these questions!

1.Research subjects that are divided up based on gender, age, etc. to be compared to people of the same group is what type of design experiment?

2. A biologist collects a sample of 50 snakes. The snakes have a mean length of 25 cm with a standard deviation of 5 cm. If the mean length for the population of snakes is 27 cm, what is the probability of a sample having a mean length less than 27?

3. A sample of size 35 is taken from a uniformly distributed population. The mean of the population is 40 and the standard deviation is 3. Find the standard deviation of the sample.

Please help me with these!