In: Math
For 300 trading days, the daily closing price of a stock (in $) is well modeled by a Normal model with mean $196.38 and standard deviation $7.13.
According to this model, what is the probability that on a randomly selected day in this period the stock price closed as follows.
a) above $203.51?
b) below $210.64?
c) between $182.12 and $210.64?
d) Which would be more unusual, a day on which the stock price closed above $206 or below $180?
Solution:-
a) The probability that on a randomly selected day in this period the stock price closed is above 203.51 is 0.1587.
x = 203.51
By applying normal distribution:-
z = 1.0
P(z > 1.0) = 0.1587
b) The probability that on a randomly selected day in this period the stock price closed is below 210.64 is 0.977.
x = 210.64
By applying normal distribution:-
z = 2.0
P(z < 2.0) = 0.977
c) The probability that on a randomly selected day in this period the stock price closed is between $182.12 and $210.64 0.954 .
x1 = 182.12
x2 = 210.64
By applying normal distribution:-
z1 = - 2.0
z2 = 2.0
P( -2.0 < z < 2.0) = P(z > -2.0) - P(z > 2.0)
P( -2.0 < z < 2.0) = 0.977 - 0.023
P( -2.0 < z < 2.0) = 0.954
d) The day on which the stock price closed below $180 is more unusual.
x = 206
By applying normal distribution:-
z = 1.35
P(z > 1.35) = 0.089
x = 180
By applying normal distribution:-
z = -2.29
P(z < -2.29) = 0.011