In: Math
For 300 trading days, the daily closing price of a stock (in $) is well modeled by a Normal model with a mean of
$197.12197.12 and a standard deviation of
$7.187.18. 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 $204.30204.30?
b) below $211.48211.48?
c) between $182.76182.76 and $211.48211.48?
Solution :
Given that ,
mean = = 197.12
standard deviation = = 7.18
(a)
P(x > 204.30) = 1 - P(x < 204.30)
= 1 - P((x - ) / < (204.30 - 197.12) / 7.18)
= 1 - P(z < 1)
= 1 - 0.8413
= 0.1587
P(x > 204.30) = 0.1587
Probability = 0.1587
(b)
P(x < 211.48) = P((x - ) / < (211.48 - 197.12) / 7.18)
= P(z < 2)
Using standard normal table,
P(x < 2) = 0.9772
Probability = 0.9772
(c)
P(182.76< x < 211.48) = P((182.76 - 197.12)/ 7.18) < (x - ) / < (211.48 - 197.12) / 7.18) )
= P(-2 < z < 2)
= P(z < 2) - P(z < -2)
= 0.9772 - 0.0228
= 0.9544
Probability = 0.9544