4. If X is a random variable and has a normal distribution with mean µ and standard deviation σ,
then the Empirical Rule says the following:
About 68% of the x values lie between –1σ and +1σ of the mean µ (within one standard
deviation of the mean).
About 95% of the x values lie between –2σ and +2σ of the mean µ (within two standard
deviations of the mean).
About 99.7% of the x values lie between –3σ and +3σ of the mean µ(within three standard
deviations of the mean).
The z-scores for +1σ and –1σ are +1 and –1, respectively.
The z-scores for +2σ and –2σ are +2 and –2, respectively.
The z-scores for +3σ and –3σ are +3 and –3 respectively.
5. If a stock has a mean return of 8% and a Std. Dev of 10%. Find its max and min
value upto 3 std dev assuming that the data points are distributed normally
Mean = μ = 0.08
Std dev = σ = 0.1
Formula for min and max value μ ± zσ
Min and max values for 1 std dev
μ ± zσ = μ ± 1σ = 0.08 ± 1*0.1 = -0.02 to 0.18 (About 68% of the x values lie Between -0.02 and 0.18)
Min and max values for 2 std dev
μ ± zσ = μ ± 2σ = 0.08 ± 2*0.1 = -0.12 to 0.28 (About 95% of the x values lie Between -0.02 and 0.18)
Min and max values for 3 std dev
μ ± zσ = μ ± 3σ = 0.08 ± 3*0.1 = -0.22 to 0.38 (About 99.7% of the x values lie Between -0.02 and 0.18)
6. What is the probability that a stock with mean return of 8% and standard
deviation of 10% would yield a return of 6% or less.
The probability that return is less than 6% [P(x<6)=0.4207]
7. What is the probability that a stock with mean return of 8% and standard
deviation of 10% would yield a return of 15% or less.
The probability that return is less than 15% [P(x<15)=0.7580]
8. What is the probability that a stock with mean return of 8% and standard deviation of 10% would
yield a return between 12% and 18%
[P(x<12)=0.6554]
[P(x<18)=0.8413]
[P(12<x<18) = 0.8413 – 0.6554 = 0.1859]
9. Covariance and correlation
• Covariance: Co-movement between two
assets
• Correlation: Standardized version of
covariance
10. Covariance (Historical data)
Given below are the closing stock prices of two companies. Find
out the covariance between them.
Year Raincoat comp Sunglass comp
2017 100 300
2018 90 330
2019 80 350
2020 75 360
11. Covariance (Probabilistic data)
You bought a share of Raincoat company for Rs 120 and one
share of Sunglass company for Rs 280. Under the current
scenario, three probabilities of share price movements for the
companies are likely
Prob RC SC
0.3 100 300
0.2 90 330
0.5 80 350