The amounts of monthly electric and gas bills for a 3-bedroom townhouse in Calgary have a distribution with a mean of $315 and a standard deviation of $35.

Find the probability that:

a) An individual townhouse pays less than $305. Include a labeled sketch of the curve. [2 marks]

b) The mean amount of bills for a random sample of 75 households will be less than $305. Include a labeled sketch of the curve. [3 marks]

c) The mean amount of bills for a random sample of 55 households will be less than $325. Include a labeled sketch of the curve.