For women aged 18-24, systolic blood pressures (in mm Hg) are normally distributed with a mean of 114.8 mm and a standard deviation of 13.1 mm. Round your answers to the nearest tenth (2 decimal places).

a) If a women between the ages of 18 and 24 is randomly selected, find the probability that her systolic blood pressure is above 120 mm.

b) If 12 women in that age bracket are randomly selected, find the probability that their mean systolic blood pressure is greater than 120 mm.

c) Thoroughly explain why increasing the sample size changes the probability value.