Adding another card with value $25 would decrease the standard deviation
because it is closer to the mean the the current standard deviation.
The d value is going to be -3 because you have to compute the differences of all the adjacent terms. 2-5=-3 -1-2=-3 -4-(-1)=-3 -7-(-4)=-3 The difference between all the adjacent terms is the same and equal to -3
0.25 is the probability that you would select a score between 300 and 700. I used the empirical rule when i solved this.
