To get this you take the £86 and multiply it by 0.65 because with the 35% sale you are paying for 65% of the item. You get this number by subtracting 35 from 100 and convert it into a decimal.
The axis of symmetry for this parabola is the x-axis. The general form of the equation is: 4p(x-h) = (y-k)^2 where the focus has the coordinates of (h+p,k)
Manipulating the given equation to the general form: 4(1/3)(x-7)^2 = (y - 0)^2
Therefore the coordinates of the focus is: (7+(1/3),0)
Assuming a standard normal distribution, the positive value of interest will be that corresponding to the 50 + 36/2 = 68th percentile. A suitable probability calculator will give that value as 0.46770.
The values that are within ±0.46770 standard deviations from the mean will have a probability of 0.36.
