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Maths Presentation

Probability

Probability

What is Probability ?

Probability is a branch of Mathematics that

deals with calculating the likelihood of a given

event's occurrence, which is expressed as a

number between 1 and 0.

Example

Playing Cards

If you draw a card from a standard deck of

cards , what is the probability of not getting a

heart?

Example

Bag with Marbles

If a bag contains 5 white and 7 red marbles,

what is probability of getting a red marble ?

Real Life Problems

Real Life Problems

  • Size of independent set in a graph

  • IQ Problem

  • Coupon Collector Problem

Compute the lower bound on the size of the largest Independent Set of Graph.

Problem - 1

The largest independent set is

What is an independent set ?

Independent Set

Degree of vertex of a Graph

Degree of Vertex of a Graph

Cycle Graph

Largest Independent set in a Cycle Graph is of [n/2] size 

where n is the total number of vertices.

Procedure 1

n = total number of vertices

I  = Independent Set =

S =  {v1 , v2 , v3 , …........vn } 

Repeat the following till S is not empty :

  • Remove the lowest index vertex v from S and add it to I.
  • Remove all the neighbours of v from S if they are not already removed.
  • Repeat

Procedure 2

Let's bound the expected size of I 

v= a vertex or node of graph

Iv = an indicator variable which indicates whether or not v belongs to I i.e. Iv = 1 if it does belong or 0

V belongs to I if none of its neighbour appear before it in the permunation. This happens with probability 1/dv.

There must be atleast permutation for which

 the size of I is at least equal to its expectation.

Example

Initially, I = { }

Let S = {2 , 6 , 7 , 5 , 4 , 3 }

Removing lowest index vertex 2 and its neighbours :

I = { 2 }

S = { 7 , 5 , 3 }

Removing lowest index vertex 7 and its neighbours :

I = { 2 , 7 }

S = {  }

=       = 2.66 

IQ Problem...

Problem - 2

Assume that IQ scores are normally distributed, with a mean µ of 100 and standard deviation   of 15. What is the probability that a randomly selected person has an IQ score greater than 110?

Normal Distribution

Normal Distribution...

Normal distribution, also known as the Gaussian distribution, is a probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean.

Solution

Solution...

Coupon Collector Problem

Problem - 3

Motto : To collect all the coupons and win

The Problem

Coupon Collector Problem

  • In probability , the coupon collector's problem describes "collect all coupons and win" contests

  • It asks the following question: If each box of a brand of cereals contains a coupon, and there are n different types of coupons, what is the probability that more than t boxes need to be bought to collect all n coupons?

  • The mathematical analysis of the problem reveals that the expected number of trials needed grows as O(nlog(n)).

  • For example, when n = 50 it takes about 225[b] trials on average to collect all 50 coupons

Description

Figure describing the situation :

Solution

Solution

Let T be the time to collect all n coupons, and let ti be the time to collect the i-th coupon after i − 1 coupons have been collected.

Think of T and ti as random variables.

By the linearity of expectations we have :

Here Hn is the n-th harmonic number. Using the asymptotics of the harmonic numbers, we obtain :

where , is the Euler–Mascheroni constant.

Now one can use the Markov inequality to bound the desired probability:

Thank You !

Name

Roll No.

Created by

LIT2019072

LIT2019073

LIT2019074

LIT2019075

LIT2019076

LIT2019077

Anu Kumari

Ayushi Panth

Nishan Singh

Kanu priya

Rajat Napalchyal

Harsh Tiwari

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