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Probability Test - 14

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Probability Test - 14
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  • Question 1
    1 / -0
    Let $$\mathrm{E}^{\mathrm{c}}$$ denote the complement of an event $$\mathrm{E}$$. Let $$\mathrm{E},\ \mathrm{F},\ \mathrm{G}$$ be pairwise independent events with $$\mathrm{P}(\mathrm{G})>0$$ and $$\mathrm{P}(\mathrm{E}\,\mathrm{\cap}\,\mathrm{F}\,\mathrm{\cap}\,\mathrm{G}) =0$$. Then $$\mathrm{P}(\mathrm{E}^{\mathrm{c}}\,\mathrm{\cap}\,\mathrm{F}^{\mathrm{c}}|\mathrm{G})$$ equals 
    Solution

  • Question 2
    1 / -0
    A signal which can be green or red with probability $$\displaystyle \frac{4}{5}$$ and $$\displaystyle \frac{1}{5}$$ respectively, is received by station $$\mathrm{A}$$ and then transmitted to station $$\mathrm{B}$$. The probability of each station receiving the signal correctly is $$\displaystyle \frac{3}{4}$$. If the signal received at station $$\mathrm{B}$$ is green,  then the probability that the original signal was green is
    Solution
    Let Event $$\mathrm{G}=$$ original signal is green
    $$\mathrm{E}_{1}=\mathrm{A}$$ receives the signal correct
    $$\mathrm{E}_{2}=\mathrm{B}$$ receives the signal correct
    $$\mathrm{E}=$$ signal received by $$\mathrm{B}$$ is green
    $$\mathrm{P}$$(signal received by $$\mathrm{B}$$ is green)
    $$=\mathrm{P}(\mathrm{G}\mathrm{E}_{1}\mathrm{E}_{2})+\mathrm{P}(\mathrm{G}\overline{\mathrm{E}}_{1}\overline{\mathrm{E}}_{2})+\mathrm{P}(\overline{\mathrm{G}}\mathrm{E}_{1}\overline{\mathrm{E}}_{2})+\mathrm{P}(\overline{\mathrm{G}}\ 
     \overline{\mathrm{E}}_{1}\mathrm{E}_{2})$$

    $$ = \displaystyle \left( \frac{4}{5}\times\frac34\times\frac34 \right) +\left( \frac45\times\frac14\times\frac14 \right) +\left( \frac15\times\frac34\times\frac14 \right )+\left(\frac15\times\frac14\times\frac34 \right)$$

    $$\displaystyle \mathrm{P}(\mathrm{E})=\frac{46}{80}$$
    $$\mathrm{P}(\mathrm{G}/\mathrm{E}) =\displaystyle \frac{\displaystyle \left( \frac{4}{5}\times\frac34\times\frac34 \right) +\left( \frac45\times\frac14\times\frac14 \right)}{\dfrac{46}{80}}=\frac{20}{23}$$
  • Question 3
    1 / -0

    Directions For Questions

    There are five students $$S_1, S_2, S_3, S_4$$ and $$S_5$$ in a music class and for them are five seats $$R_1, R_2, R_3, R_4$$ and $$R_5$$ arranged in a row, where initially the seat $$R_i$$ is allotted to the student $$S_i$$, $$i=1, 2, 3, 4, 5$$. But, on the examination day, the five students are randomly allotted the five seats.

    ...view full instructions

    For $$i=1, 2, 3, 4$$ let $$T_i$$ denote the event that the students $$S_i$$ and $$S_{i+1}$$ do NOT sit adjacent to each other on the day of the examination. Then the probability of the event $$T_1 \cap T_2 \cap T_3 \cap T_4$$ is?
    Solution
    $$n(T_1 \cap T_2 \cap T_3 \cap T_4)=$$Total $$-n(\bar{T_1}\cup \bar{T_2}\cup \bar{T_3}\cup \bar{T_4})$$
    $$=5!-\left({^4C_1}4!2!-\left({^3C_1}.3!2!+{^3C_1}3!2!2!\right)+\left({^2C_1}2!2!+{^4C_1}.2.2!\right)-2\right)$$
    $$=14$$
    Probability $$=\displaystyle\frac{14}{5!}=\frac{7}{60}$$.
  • Question 4
    1 / -0

    Directions For Questions

    There are five students $$S_1, S_2, S_3, S_4$$ and $$S_5$$ in a music class and for them are five seats $$R_1, R_2, R_3, R_4$$ and $$R_5$$ arranged in a row, where initially the seat $$R_i$$ is allotted to the student $$S_i$$, $$i=1, 2, 3, 4, 5$$. But, on the examination day, the five students are randomly allotted the five seats.

    ...view full instructions

    The probability that, on the examination day, the student $$S_1$$ gets the previously allotted seat $$R_1$$ and None of the remaining students gets the seat previously allotted to him/her is?
    Solution
    Required probability $$=\displaystyle\frac{4!\left(\displaystyle\frac{1}{2!}-\frac{1}{3!}+\frac{1}{4!}\right)}{5!}=\frac{9}{120}=\frac{3}{40}$$.
  • Question 5
    1 / -0
    A bag contains 12 balls out of which x are white.If one ball is drawn at random, what is the probability it will be a white ball?
    Solution
    Total number of balls = 12
    Number of white balls = x
    P (white ball) = $$= \displaystyle \frac{x}{12}$$
  • Question 6
    1 / -0
    A pack of playing cards was found to contain only $$51$$ cards. If the first $$13$$ cards which are examined are all red, then the probability thatthe missing card is black, is
    Solution
    $$Total\quad number\quad of\quad cards=52\\ Number\quad of\quad lost\quad cards=1\\ 13\quad cards\quad are\quad surely\quad red\quad therfore,\quad from\quad the\quad remaining\quad 39\quad cards\quad 26\quad are\quad black\quad and\quad 13\quad are\quad red\\ So\quad probability\quad of\quad lost\quad card\quad being\quad black\quad =\frac { \left( 26\\ 1 \right)  }{ \left( 39\\ 1 \right)  } =\frac { 26 }{ 39 } =\frac { 2 }{ 3 } $$
  • Question 7
    1 / -0
    If $$P(A) + P(B) = 1$$; then which of the following option explains the event $$A$$ and $$B$$ correctly ?
    Solution
    Since $$P(A) +P(B) = 1$$
    $$\therefore A \cap B = 0$$.
    Thus, event $$A$$ and $$B$$ are mutually exclusive, exhaustive and complementary events.
    Hence, option $$A$$ is correct.
  • Question 8
    1 / -0
    A bag contains 40 balls out of which some are red, some are blue and remaining are black. If the probability of drawing a red ball is $$\displaystyle \frac{11}{20}$$ and that of blue ball is $$\displaystyle \frac{1}{5}$$, then the number of black ball is?
    Solution
    Let no. of red balls = x, no. of blue balls =y and no.of black balls = z.
    Probability of drawing a red ball = P (red ball) =$$\displaystyle \frac{11}{20} =\frac{x}{40}$$
    $$\Rightarrow $$ x=22
    Probability of drawing a blue ball = P (Blue ball) = $$\displaystyle \frac{1}{5} =\frac{y}{40}$$
    $$\Rightarrow$$ y=8
    $$\therefore$$ No of black balls = 40- 22 -8 =10
  • Question 9
    1 / -0
    There are 50 marbles of 3 colors: blue yellow and black The probability of picking up a blue marble is 3/10 and that of picking up a yellow marble is 1/2 The probability of picking up a black ball is 
    Solution
    P(blue)=$$\displaystyle \frac{3}{10}=\frac{15}{50},$$i.e., there are 15 blue marbles
    P(yellow)=$$\displaystyle \frac{1}{2}=\frac{25}{50},$$i.e., there are 25 yellow marbles
    $$\displaystyle \therefore $$ Number of black marbles=10
    $$\displaystyle \therefore $$ P(black)=$$\displaystyle \frac{10}{50}=\frac{1}{5}$$
  • Question 10
    1 / -0
    A bag contains six red four green and eight white balls If a ball is picked at random the probability that it is not white is
    Solution
    Number of balls that are not white=10
    Total=18
    $$\displaystyle \therefore $$ P(not white)=$$\displaystyle \frac{10}{18}=\frac{5}{9}$$
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