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Probability Test - 15

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Probability Test - 15
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  • Question 1
    1 / -0
    There are $$40$$ students in a class and their results is presented as below :
    Result (Pass/Fail)PassFail
    Number of Students$$30$$$$10$$

    If a student chosen at random out of the class, find the probability that the student has passed the examination
    Solution
    Total number of chances $$= 40$$
    Chances or trials which favour a student to pass $$= 30$$
    The probability of the required event, i.e., the student has passed the examination $$=$$ $$ \displaystyle \frac{30}{40} $$ $$= 0.75$$
  • Question 2
    1 / -0

    $$400$$ students of class $$X$$ of a school appeared in a test of $$100$$ marks in the subject of social
    studies and the data about the marks secured is as below :

                Marks
              secured
    Number of
    Students
                $$0-25$$     $$50$$
              $$26-50$$    $$220$$
              $$51-75$$    $$100$$
            Above $$75$$      $$30$$
    Total number of students    $$400$$

    If the result card of a student he picked up at random, what is the probability that the student has secured more than $$50$$ marks.

    Solution
    Total number of students, i.e , the total frequency $$= 400$$
    The total number of students who secured more than $$50$$ marks $$100 + 30 = 130$$
    Probability that the marks secured are more than $$50 =$$ $$ \displaystyle \frac{130}{400} $$ = $$ \displaystyle \frac{1.3}{4} $$ = $$0.325$$
  • Question 3
    1 / -0

    There are $$40$$ students in a class and their results is presented as below :

    Result (Pass/Fail)PassFail
    Number of Students$$30$$$$10$$

    If a student chosen at random out of the class, find the probability that the student has passed the examination.

    Solution
    Total number of chances $$= 40$$
    Chances or trials which favour a student to pass $$= 30$$
    The probability of the required event, i.e., the student has passed the examination $$= \displaystyle \frac{30}{40} = 0.75$$
  • Question 4
    1 / -0

    A coin is tossed $$150$$ times and the outcomes are recorded. The frequency distribution of the outcomes $$H$$ (i.e, head) and $$T$$ (i.e, tail) is given below :

    Outcome$$H$$$$T$$
    Frequency$$85$$$$65$$

    Find the value of $$P(H)$$, i.e, probability of getting a head in a single trial.

    Solution
    Total number of trials $$=$$$$150$$
    Chances or trials which favour the outcome $$H =$$ $$85$$
    $$P (H) =$$ $$ \displaystyle \frac{85}{150} $$ = $$0.567$$ (approx)
  • Question 5
    1 / -0
    A die having six faces is tossed $$80$$ times and the data is as below:

    Outcome



    $$1$$



    $$2$$



    $$3$$



    $$4$$



    $$5$$



    $$6$$



    Frequency



    $$10$$



    $$20$$



    $$10$$



    $$28$$



    $$8$$



    $$4$$


    Find $$P (1) $$.

    Solution
    Since, Total tosses $$=$$ $$80$$
    Getting no. of $$1$$'s in total tosses $$=$$ $$10$$
    $$\therefore$$ P$$(1) = \dfrac {10}{80} = 0.125 $$
  • Question 6
    1 / -0
    A die is thrown $$200$$ times and the outcomes $$1, 2, 3, 4, 5, 6$$ have frequencies as below:

    Outcome



    $$1$$



    $$2$$



    $$3$$
     


    $$4$$



    $$5$$



    $$6$$



    Frequency



    $$40$$



    $$38$$



    $$43$$



    $$29$$



    $$28$$



    $$22$$


    Find the probabilities of getting a number more than $$1$$ and less than $$6$$ in a toss (trial).

    Solution
    Since, Total cases $$= 200$$
    Getting a no. more than $$1$$ and less than $$6\, (2,3,4,5) = 38+43+29+28 = 138$$
    $$\therefore $$ probability $$=$$$$\dfrac {138}{200} = 0.69 $$
  • Question 7
    1 / -0

    There are $$500$$ packets in a large box and each packet contains $$4$$ electronic devices in it. On testing, at the time of packing, it was noted that there are some faulty pieces in the packets. The data is as below:

    No. of faulty
    devices in a packet
    Number of packets
                     $$0$$             $$300$$
                     $$1$$             $$100$$
                     $$2$$               $$50$$
                     $$3$$               $$30$$
                     $$4$$               $$20$$
    Total number of packets              $$500$$

    If one packet is drawn from the box, what is the probability that all the four devices in the packet are without any fault?

    Solution
    When the packet has all the four devices without fault, it means the number of faulty devices in the packet is $$0$$.
    Number of chances which are favourable to $$0$$ are $$300$$ as given in the table above. Thus, the probability of packet containing all the four devices without any fault $$=$$ $$ \displaystyle \frac{300}{500} $$ $$=$$ $$ \displaystyle \frac{3}{5} $$$$ =$$ $$0.6$$
  • Question 8
    1 / -0
    In a shooting game, John shoots the balls $$20$$ times out of $$40$$ trials. What is the empirical probability of the shooting event?
    Solution
    The total number of trials $$= 40$$
    John shoots the balls only $$20$$ times.
    So, the empirical probability formula is as follows,
    $$P(E) =$$ $$\dfrac{20}{40}= \dfrac{1}{2}$$
  • Question 9
    1 / -0

    Directions For Questions

    10  bags of wheat flour each marked 5 kg, actually contained weights of flour (in kg)
    $$5.05, 5.08, 5.03, 5.00, 5.06, 5.08, 4.98, 5.04, 5.07, 5.00$$

    ...view full instructions

    Find probability of bag chosen out random contains more than $$5\ kg$$.
    Solution
    Total number of bags $$=10$$
    Number of bags contain flour more than $$5kg =7$$ 
    They are :$$5.05,5.08,5.03,5.06,5.08,5.04,5.07$$

    $$P(A)=\dfrac {Number\ of\ favorable\ outcomes}{Total\ Number\ of\ possible\ outcomes} $$

    $$\therefore P(A)=\dfrac{7}{10}=0.7$$
  • Question 10
    1 / -0
    What is the probability that there are $$5$$ Mondays in the month of February 2016?
    Solution
    There are $$29$$ days in February $$2016$$.
    There will be $$4$$ weeks and $$1$$ day. This one day can be any one from mon, tue, wed, thurs, fri, sat, sun.
    So, probability of having $$5$$ Mondays $$=\dfrac { 1 }{ 7 } $$
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