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Introduction to Probability

Please to solve the following questions:

1. A positive integer lessthan 21 is chosen at random. What is the probability

that it is a multiple of 3?

2. Which of the following numbers can represent the probability of an event?

a. 3.1415/2 b. 1/3.1415 c. 1/2^1

3.A card is drawn at random from a pack of well-shuffled playing cards. What

is the probability of getting a Jack or a spade?

4.If two dice are rolled, the probability of getting a sum divisible by 4 is

5.A series of literature books contains 4 volumes, and they are arranged on a bookshelf at random. Whant is the probability that the first and the last volume are placed at both ends?

1 個解答

評分
  • TamTam
    Lv 7
    1 十年前
    最愛解答

    1.

    P(multiple of 3)

    =P(getting 3,6,9,12,15,18)

    =6/20

    =3/10

    2.

    1/3.1415 and 1/2^1 can represent a probability of event.

    (The values of above numbers are between 0 and 1)

    3.

    P(Jack or spade)

    =P(spade)+P(Jack)-P(spade Jack)

    =13/52+4/52-1/52

    =16/52

    =4/13

    4.

    P(divisible by 4)

    =P(get 4)+P(get 8)+P(get 12)

    =P(get (1,3)or(2,2)or(3,1))+P(get (2,6)or(3,5)or(4,4)or(5,3)or(6,2))+P(get(6,6))

    =3/36+5/36+1/36

    =9/36

    =1/4

    5.

    P(first, last volume are at both ends)

    =P(first volume at end A, then last volume at end B)+P(first volume at end B then last volume at end A)

    =(1/4)(1/3)+(1/4)(1/3)

    =1/12+1/12

    =1/6

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