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 TOPIC : Normal Distribution
------------------------------------------------
Made by : Noor-ul-ain
 Normal distribution
 Normal curve
 Characteristics
 Normal random variable
 Standard normal distribution
 Standard scores
 Applications
Definition:
Normal distribution, also known as the Gaussian
distribution, is a probability distribution that is symmetric about
the mean, showing that data near the mean or more frequent in
occurrence than data from the mean.
In graph form, normal distribution will appear as bell curve.
History:
In 1733, DeMoivre derived the mathematical equation of
normal curve. It is often referring to as the Gaussian Distribution in
honor of Gauss (1777-1855), who also derived its equation from a
study of errors in repeated measurements of the same quantity.
Definition:
A normal curve is a bell-shaped curve which shows
the probability distribution of a continuous random variable.
Moreover, the normal curve represents a normal distribution.
The total area under the normal curve logically represents the
sum of all probabilities for a random variables. Hence, the area
under the normal curve is one. Also, the standard normal curve
represents a normal curve with mean 0 and standard deviation 1.
Thus, the parameters involved in a normal distributions is mean (µ)
and standard deviation (Ϭ).
Characteristics of a Normal Curve:
 The values of mean, median and mode are same
 It represents a unimodal distribution as it has only one peak.
 It shows a symmetric distribution as 50% of the data set lies
on the left side of the mean and 50% of the data set lies on
the right side of the mean.
 Empirical rule: 68% of the data fall within µ ± б , 95% of the
data fall within µ ± 2б and 99.7% of the data fall within µ ±
3б.
Some examples for normal distribution are given below:
• Heights/weights of the subjects under study
• IQ scores of the students
• Test scores of the students
A continuous random variable X having the bell-shaped
distribution as shown in the fig, is called a normal random
variable. The mathematical equation for the probability
distribution of the normal variable depends upon the two
parameters µ and б, its mean and standard deviation. Hence, we
denote the values of the density function of X by n(x; µ, б).
Definition :
The distribution of a normal random
variable with mean zero and standard
deviation equal to one is a standard normal
distribution .
 Definition :
The value on the standard normal
distribution is known as a standard score or a
Z-score .
A standard score represents a number
of standard deviations above or below the
mean that a specific observation falls .
Z-score is equal to ,
z = x-µ
б
where x is the random variable and µ is the mean and б is the
standard deviation .
A radar unit is used to measure speed of cars on the motorway .
The speed are normally distributed with a mean of 90 km/hr
and standard deviation 10 km/hr . What is the probability
that a car picked at random is travelling at more than 100km
/hr ?
answer :
Let X be the random sample, so X has µ=90 , б=10
Then we must find P(x>100)
For x=100 , so z=1
For P(x>90)=P(Z>1)= total area –area to the left z=1
=1-0.8413 = 0.1587
The probability P(X>100) is equal to 0.1587
(1) The main reason that the normal distribution is so
popular is because it works . The reason that it works is
really because of the central limit theorem .
(2) A standard normal distribution can often be used to
solve practical application problems like IQ level of
students .
(3) In order to use it , the variables must be normally (or
approximately normally) distributed (bell shaped
graph).
……………
Normal distribution

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Normal distribution

  • 1.  TOPIC : Normal Distribution ------------------------------------------------ Made by : Noor-ul-ain
  • 2.  Normal distribution  Normal curve  Characteristics  Normal random variable  Standard normal distribution  Standard scores  Applications
  • 3.
  • 4. Definition: Normal distribution, also known as the Gaussian distribution, is a probability distribution that is symmetric about the mean, showing that data near the mean or more frequent in occurrence than data from the mean. In graph form, normal distribution will appear as bell curve. History: In 1733, DeMoivre derived the mathematical equation of normal curve. It is often referring to as the Gaussian Distribution in honor of Gauss (1777-1855), who also derived its equation from a study of errors in repeated measurements of the same quantity.
  • 5. Definition: A normal curve is a bell-shaped curve which shows the probability distribution of a continuous random variable. Moreover, the normal curve represents a normal distribution. The total area under the normal curve logically represents the sum of all probabilities for a random variables. Hence, the area under the normal curve is one. Also, the standard normal curve represents a normal curve with mean 0 and standard deviation 1. Thus, the parameters involved in a normal distributions is mean (µ) and standard deviation (Ϭ).
  • 6.
  • 7. Characteristics of a Normal Curve:  The values of mean, median and mode are same  It represents a unimodal distribution as it has only one peak.  It shows a symmetric distribution as 50% of the data set lies on the left side of the mean and 50% of the data set lies on the right side of the mean.  Empirical rule: 68% of the data fall within µ ± б , 95% of the data fall within µ ± 2б and 99.7% of the data fall within µ ± 3б.
  • 8. Some examples for normal distribution are given below: • Heights/weights of the subjects under study • IQ scores of the students • Test scores of the students
  • 9. A continuous random variable X having the bell-shaped distribution as shown in the fig, is called a normal random variable. The mathematical equation for the probability distribution of the normal variable depends upon the two parameters µ and б, its mean and standard deviation. Hence, we denote the values of the density function of X by n(x; µ, б).
  • 10. Definition : The distribution of a normal random variable with mean zero and standard deviation equal to one is a standard normal distribution .
  • 11.
  • 12.  Definition : The value on the standard normal distribution is known as a standard score or a Z-score . A standard score represents a number of standard deviations above or below the mean that a specific observation falls .
  • 13. Z-score is equal to , z = x-µ б where x is the random variable and µ is the mean and б is the standard deviation .
  • 14. A radar unit is used to measure speed of cars on the motorway . The speed are normally distributed with a mean of 90 km/hr and standard deviation 10 km/hr . What is the probability that a car picked at random is travelling at more than 100km /hr ? answer : Let X be the random sample, so X has µ=90 , б=10 Then we must find P(x>100) For x=100 , so z=1 For P(x>90)=P(Z>1)= total area –area to the left z=1 =1-0.8413 = 0.1587 The probability P(X>100) is equal to 0.1587
  • 15. (1) The main reason that the normal distribution is so popular is because it works . The reason that it works is really because of the central limit theorem . (2) A standard normal distribution can often be used to solve practical application problems like IQ level of students . (3) In order to use it , the variables must be normally (or approximately normally) distributed (bell shaped graph). ……………