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Probability Test - 29

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Probability Test - 29
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  • Question 1
    1 / -0
    An experiment can result in only 3 mutually exclusive events A, B and C. If  $$ \displaystyle P\left ( A \right )=2P\left ( B \right )=3P\left ( C \right ), $$ then $$ \displaystyle P\left ( A \right ) $$ equals
    Solution
    since the events A,B and C are mutually exclusive 
    Hence $$P\left( A\cap B \right) =P\left( B\cap C \right) =P\left( C\cap A \right) =P\left( A\cap B\cap C \right) =0\\ Also\quad P\left( A\cup B\cup C \right) =1$$
    $$\because P\left( A\cup B\cup C \right) =P\left( A \right) +P\left( B \right) +P\left( C \right) -P\left( A\cap B \right) -P\left( B\cap C \right) -P\left( C\cap A \right) -P\left( A\cap B\cap C \right) \\ \Rightarrow 1=P\left( A \right) +\dfrac { P\left( A \right)  }{ 2 } +\dfrac { P\left( A \right)  }{ 3 } \\ \Rightarrow \dfrac { 11 }{ 6 } P\left( A \right) =1\\ \Rightarrow P\left( A \right) =\dfrac { 6 }{ 11 } $$
  • Question 2
    1 / -0
    A die is thrown :
    $$P$$ is the event of getting an odd number.
    $$Q$$ is the event of getting an even number.
    $$R$$ is the event of getting a prime number.
    Which of the following pairs is mutually exclusive?
    Solution
    Let $$S$$ be the sample space
    $$S=\{1,2,3,4,5,6\}$$
    $$n(S)=6$$
    $$P$$ is the event of getting an odd number
    $$\therefore P=\{1,3,5\}\implies n(P)=3$$
    $$Q$$ is the event of getting an even number
    $$\therefore Q=\{2,4,6\}\implies n(Q)=3$$
    $$R$$ is the vent of getting a prime number
    $$\therefore R=\{2,3,5\}\implies n(R)=3$$
    The set $$S$$ contains two types of numbers even and odd
    We have, $$P=S-Q$$ and $$Q=S-P$$
    $$\therefore n(P)$$ and $$n(Q)$$ both are complementary.
    Two events are mutually exclusive if they are disjoint
    Now, $$P\cap Q=\phi$$
    $$\implies P$$ and $$Q$$ are disjoint i.e. they don't have common elements.
    Hence, $$P$$ and $$Q$$ are mutually exclusive.
  • Question 3
    1 / -0
    $$A$$ and $$ B$$ are events such that $$\displaystyle p(A \cup B) =3/4,P(A\cap B)=\frac{1}{4},P(\bar{A})=\frac{2}{3}$$, then $$\displaystyle P((\bar{A}\cap B)$$ equals
    Solution
     Given $$\displaystyle P(A\cup B)=3/4$$
    $$\displaystyle  P(A\cap B)=1/4$$ $$\displaystyle P(\bar{A})=2/3\therefore P(B)=\frac{2}{3}$$
    By using $$\displaystyle P(B) =P(A\cup B)+P(A\cap B)-P(A)$$
    $$\displaystyle\therefore P(\bar{A}\cap B)=\frac{2}{3}-\frac{1}{4}=\frac{5}{12}$$
  • Question 4
    1 / -0
    Form two digit numbers using the digit $$0,1,2,3,4,5$$ without repeating the digits.
    $$P$$ is the event that the number so formed is even.
    $$Q$$ is the event that the number so formed is divisible by $$3$$.
    $$R$$ is the event that the number so formed is greater than $$50$$.
    $$S$$ is the sample space.
    Which of the following options is correct?
    Solution
    The given digits are $$0,1,2,3,4,5$$
    Number of two digit numbers that can be formed, as first place can be filed with 5 numbers and second place can be filed with another 5 numbers; $$5 \times 5 = 25$$
    Now, number is an even number, with 0 at the end there can be $$5$$ numbers, with $$2$$ at the end there can be $$4$$ numbers and with $$4$$ at the end there can be $$4$$ numbers. Hence, total numbers which are even $$= 4 + 4 + 5 = 13$$
    Numbers divisible by $$3$$ are, $$12, 15, 21, 24, 30, 42, 45, 51, 54$$
    Thus, total numbers are, $$9$$
    There are only $$4$$ number, viz. $$51, 52,53,54$$ which are greater than $$50$$
    Hence, $$n(S) = 25, n(P) = 13, n(Q) = 9, n (R) = 4$$
  • Question 5
    1 / -0
    If $$P(A)\, =\, \displaystyle \frac{3}{4} ,\, P(B')\, =\, \frac{1}{3}\, and\, P(A \cap B)\, =\, \frac{1}{2}\,$$ then find $$P(A \cup B)$$.
    Solution
    Given that:
    $$P(A)=\cfrac34, P(B')=\cfrac13$$ and $$P(A\cap B)=\cfrac12$$

    To Find:
    $$P(A\cup B)=?$$

    Solution:
    $$P(B)=1-P(B')=1-\cfrac13=\cfrac23$$

    $$P(A\cup B)=P(A)+P(B)-P(A\cap B)$$

    $$=\cfrac34+\cfrac23-\cfrac12$$

    $$=\cfrac{11}{12}$$

    Hence, D is the correct option.
  • Question 6
    1 / -0
    There are $$3$$ men and $$2$$ women. a 'Gramswachhatta Abhiyan' committee of two is to be formed :
    $$P$$ is event that the committee should contain at least one woman.
    $$Q$$ is event that the committee should contain one man and one women.
    $$R$$ is the event there should not be a women in the committee.
    $$S$$ is the sample space.
    Which of the following options is correct?
    Solution
    $$n(S) = 10, n(P) = 7, n(Q) = 6, n(R) = 3$$
    $$P$$ and $$ R$$ are complementary, mutually exclusive events and exhaustive events.
    $$Q$$ and $$R$$ 
    are complementary and mutually exclusive events.
  • Question 7
    1 / -0
    A card is drawn at random from well shuffled pack of $$52$$ cards. Find the probability that the card drawn is a spade:
    Solution
    Sample space $$= 52$$
    Event a card obtained is of spade $$= 13$$(spades ,$$13$$ cards of each suits)
    Probability $$=\cfrac{13}{52}$$ $$=\cfrac{1}{4}$$
  • Question 8
    1 / -0
    A and B are two events on a sample space S such that $$P(A) = 0.8 , P(B) = 0.6$$ and $$P(A \cup B) = 0.9$$ find $$(A \cap B)$$.
    Solution
    Given that:
    $$P(A)=0.8, P(B)=0.6$$ and $$P(A\cup B)=0.9$$
    To find: $$P(A\cap B)=?$$
    $$P(A\cap B)=P(A)+P(B)-P(A\cup B)$$
    $$=0.8+0.6-0.9$$
    $$=1.4-0.9$$
    $$=0.5$$
    Hence, C is the correct option.
  • Question 9
    1 / -0
    There are $$3$$ red, $$3$$ white and $$3$$ green balls in a bag. One ball is drawn at random from a bag:
    $$P$$ is the event that ball is red.
    $$Q$$ is the event that ball is not green.
    $$R$$ is the event that ball is red or white.
    $$S$$ is the sample space.
    Which of the following options is correct?
    Solution
    There are $$3$$ red balls, $$3$$ white balls and $$3$$ green balls.
    Thus, total number of balls $$= 9$$, $$n (S) = 9$$
    $$P$$, the ball is red, $$n(R) = 3$$
    $$Q$$, the ball is not green, $$n(Q) = 9 - 3 = 6$$
    $$R$$, the ball is red or white, $$n(R) = 3 + 3 = 6$$
  • Question 10
    1 / -0
    If two coins are tossed then find the probability of the event of getting one head .
    Solution
     sample space is ={h,t} ,{t,h} 
    favourable outcomes for getting one head =$$2 $$
    probability (one head)= $$\cfrac{2}{4}$$
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