INTRODUCTION
TO
PROBABILITY
DR. FARHANA SHAHEEN
PROBABILITY
Tossing a coin Rolling a dice
Have two possibilities Have six possibilities
Head or Tail Getting 1, 2, 3, 4, 5, 6
Spinning Wheel
Probability Line
Language of Probability
Terms used in
Probability
• Certain
• Likely
• Equally likely
• Unlikely
• Impossible
Note:
• For an Event E to occur:
• Certain means 100% chances.
• Likely means more chances
• Unlikely means less chances
• Equally Likely means 50% chances
• Impossible means No chance at all
( 0 % chances)
Likely…
• More vs Less Likely
Exhaustive Events:
• In probability, a set of events is collectively exhaustive if they cover all of
the probability space: i.e., the probability of any one of them happening is
100%. If a set of statements is collectively exhaustive we know at least one
of them is true.
Mutually Exclusive Events
• Disjoint events, events that don’t have anything in common.
• Non-Mutually Exclusive Events are also
called Mutually Inclusive events.
Mutually Exclusive Events:
Activity
PROBABILITY RULES
• P(E) = 𝑷 𝑬 =
𝑵𝒖𝒎𝒃𝒆𝒓 𝒐𝒇 𝒇𝒂𝒗𝒐𝒖𝒓𝒂𝒃𝒍𝒆 𝒐𝒖𝒕𝒄𝒐𝒎𝒆𝒔
𝑵𝒖𝒎𝒃𝒆𝒓 𝒐𝒇 𝒕𝒐𝒕𝒂𝒍 𝒐𝒖𝒕𝒄𝒐𝒎𝒆𝒔
• P( Not E) = 1 – P(E)
• For any event E, 𝟎 ≤ 𝑷 𝑬 ≤ 𝟏.
• P(E) = 0 if and only if E is an impossible event. i.e. it will Never
occur.
• P(E) = 1 if and only if E is a certain event. i.e. it will Definitely occur
Ques:01
• A card is drawn at random from a standard pack of 52 playing cards.
• Find the probability of drawing :
• 1. E = a red card
• 2. E = an ace
• 3. E = the three of clubs (3 of club)
• 4. E = a card which is not the three of clubs
Ques:02
• Two joker cards are added to a standard
pack of 52 playing cards. A card is then
drawn at random from the 54 cards. Find the
probability of drawing
• (i) a red card (ii) a two
• (iii) a joker (iv) a queen or a king
• Note: A Joker card is neither a black or red
card.
Ques:03
• Raj wakes up in the morning and notices that his digital clock
reads 07:25. (ST:AB)
• At noon, he looks at the clock again. What is the probability that
• (i) the number in column A is a 4?
• (ii) the number in column B is 8?
• (iii) the number in column A is less than 6.
• (iv) the number in column B is greater than 5?
Solution:
• A = {0, 1, 2, 3, 4, 5}
• B = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
• (i) the number in column A is a 4? P(E) = 1/6
• (ii) the number in column B is 8? P(E) = 1/10
• (iii) the number in column A is less than 6. P(E) = 6/6 = 1
• (iv) the number in column B is greater than 5? P(E) = 4/10 = 2/5
Ques:04
• There are a total 117 pairs of socks in a clothes bin. Each pair of socks is
placed in a bag. The probabilities of selecting a yellow pair of socks and a
grey pair of socks at random from the bin are 2/9 and 3/13 respectively.
Find the number of pairs of socks in the bin which are
• (i) yellow,
• (ii) neither yellow nor grey.
Ques:05
• A carton contains 15 toothbrushes, out of which p have soft bristles.
After 5 more toothbrushes of soft bristles are added to the carton, the
probability of drawing a toothbrush with soft bristles becomes ¾.
Find the value of p.
Ques:06
• There are 50 students in an Auditorium, of which 2x are boys and y
are girls. After (y – 6) boys leave the Auditorium and (2x – 5) girls enter
the Auditorium, the probability of selecting a girl at random becomes
9/13. Find the value of x and y.

INTRODUCTION TO PROBABILITY.pptx

  • 1.
  • 3.
  • 4.
    Tossing a coinRolling a dice Have two possibilities Have six possibilities Head or Tail Getting 1, 2, 3, 4, 5, 6
  • 6.
  • 7.
  • 10.
  • 11.
    Terms used in Probability •Certain • Likely • Equally likely • Unlikely • Impossible
  • 12.
    Note: • For anEvent E to occur: • Certain means 100% chances. • Likely means more chances • Unlikely means less chances • Equally Likely means 50% chances • Impossible means No chance at all ( 0 % chances)
  • 13.
  • 15.
    Exhaustive Events: • Inprobability, a set of events is collectively exhaustive if they cover all of the probability space: i.e., the probability of any one of them happening is 100%. If a set of statements is collectively exhaustive we know at least one of them is true.
  • 16.
    Mutually Exclusive Events •Disjoint events, events that don’t have anything in common. • Non-Mutually Exclusive Events are also called Mutually Inclusive events. Mutually Exclusive Events:
  • 24.
  • 27.
    PROBABILITY RULES • P(E)= 𝑷 𝑬 = 𝑵𝒖𝒎𝒃𝒆𝒓 𝒐𝒇 𝒇𝒂𝒗𝒐𝒖𝒓𝒂𝒃𝒍𝒆 𝒐𝒖𝒕𝒄𝒐𝒎𝒆𝒔 𝑵𝒖𝒎𝒃𝒆𝒓 𝒐𝒇 𝒕𝒐𝒕𝒂𝒍 𝒐𝒖𝒕𝒄𝒐𝒎𝒆𝒔 • P( Not E) = 1 – P(E) • For any event E, 𝟎 ≤ 𝑷 𝑬 ≤ 𝟏. • P(E) = 0 if and only if E is an impossible event. i.e. it will Never occur. • P(E) = 1 if and only if E is a certain event. i.e. it will Definitely occur
  • 29.
    Ques:01 • A cardis drawn at random from a standard pack of 52 playing cards. • Find the probability of drawing : • 1. E = a red card • 2. E = an ace • 3. E = the three of clubs (3 of club) • 4. E = a card which is not the three of clubs
  • 30.
    Ques:02 • Two jokercards are added to a standard pack of 52 playing cards. A card is then drawn at random from the 54 cards. Find the probability of drawing • (i) a red card (ii) a two • (iii) a joker (iv) a queen or a king • Note: A Joker card is neither a black or red card.
  • 31.
    Ques:03 • Raj wakesup in the morning and notices that his digital clock reads 07:25. (ST:AB) • At noon, he looks at the clock again. What is the probability that • (i) the number in column A is a 4? • (ii) the number in column B is 8? • (iii) the number in column A is less than 6. • (iv) the number in column B is greater than 5?
  • 32.
    Solution: • A ={0, 1, 2, 3, 4, 5} • B = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9} • (i) the number in column A is a 4? P(E) = 1/6 • (ii) the number in column B is 8? P(E) = 1/10 • (iii) the number in column A is less than 6. P(E) = 6/6 = 1 • (iv) the number in column B is greater than 5? P(E) = 4/10 = 2/5
  • 33.
    Ques:04 • There area total 117 pairs of socks in a clothes bin. Each pair of socks is placed in a bag. The probabilities of selecting a yellow pair of socks and a grey pair of socks at random from the bin are 2/9 and 3/13 respectively. Find the number of pairs of socks in the bin which are • (i) yellow, • (ii) neither yellow nor grey.
  • 34.
    Ques:05 • A cartoncontains 15 toothbrushes, out of which p have soft bristles. After 5 more toothbrushes of soft bristles are added to the carton, the probability of drawing a toothbrush with soft bristles becomes ¾. Find the value of p.
  • 35.
    Ques:06 • There are50 students in an Auditorium, of which 2x are boys and y are girls. After (y – 6) boys leave the Auditorium and (2x – 5) girls enter the Auditorium, the probability of selecting a girl at random becomes 9/13. Find the value of x and y.