The following data sets are measurements made of the thickness (mm) of shells of the snail Littorina obtusata. Sample of 12 Snails were collected from sites with crab predators and without crab predators.

Habitat	Thickness (mm) of shells of the snail Littorina obtusata
With Crabs	1.02	0.88	0.75	0.94	0.81	0.98	0.79	0.83	0.86	0.93	0.91	1.05
Without Crabs	0.81	0.78	0.68	0.77	0.61	0.85	0.62	0.67	0.71	0.82	0.78	0.89

PART A: Calculate the Mean and Standard Deviation

1. Calculate the mean of both samples - snail shell thickness with crabs and without crabs.
2. Calculate the standard deviation of both samples - snail shell thickness with crabs and without crabs. Note, these are samples, so you will need to use STDEV.S in excel.
3. Draw a table to summarise your results. Do not forget to include units.
4. Which snails have thicker shells? Write a complete sentence and suggest a reason for this finding.

Write a complete sentence to identify which snails' shell thickness is more variable? PART B: Confidence Interval (9 Marks)

1. The sample without crabs is used to estimate the population mean for all snails using the Student's t-Distribution. Identify the following parameters:
   1.