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Probability Test - 17

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Probability Test - 17
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  • Question 1
    1 / -0
    Two coins are tossed $$1000$$ times and the outcomes are recorded as below:
    No of heads
    $$2$$
    $$1$$
    $$0$$
    Frequency
    $$200$$
    $$550$$
    $$250$$
    Based on this information, the probability for at most one head is $$\dfrac{a}{b}$$, where $$(a,b)=1$$. Then $$\dfrac{a}{b}$$ is
    Solution
    Total number of outcomes $$= 1000$$
    Number of favourable outcomes $$= 800$$
    Probability = $$\dfrac{800}{1000}$$ = $$\dfrac{4}{5}$$
  • Question 2
    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 packetNumber 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 3
    1 / -0

    Fifty seeds were selected at random from each of $$5$$ bags $$A, B, C, D, E$$ of seeds, and were kept under standardised conditions equally favourable to germination. After $$20$$ days, the number of seeds which had germinated in each collection were counted and recorded as follow :

    Bag$$A$$$$B$$$$C$$$$D$$$$E$$

    Number of seeds

     germinated

    $$40$$$$48$$$$42$$$$39$$$$41$$

    What is the probability of germination of

    $$(i)$$ more than $$40$$ seeds in a bag?

    $$(ii)$$ $$49$$ seeds in a bag?

    $$(iii)$$ more than $$35$$ seeds in a bag?


    Solution
    (i) Number of bags in which more than $$40$$ seeds out of $$50$$ seeds germinated $$= 3$$
    So, $$P$$ (more than $$40$$ seeds in a bag germinated) $$=$$ $$ \displaystyle \frac{3}{5} $$ $$= 0.60$$

    (ii)Number of bags in which $$49 $$ seeds germinated $$= 0$$
    So, $$P$$ ($$49$$ seeds germinated in bag) $$=$$ $$ \displaystyle \frac{0}{5} $$ $$= 0$$

    (iii) Number of bags in which more than $$35$$ seeds out $$50$$ seeds germinated $$= 5$$
    Total number of bags$$ = 5$$
    So, $$P $$(more than $$35$$ seeds in a bag germinated) $$=$$ $$ \displaystyle \frac{5}{5} $$ $$= 1$$
  • Question 4
    1 / -0

    A tyre manufacturing company kept a record of the distance covered before a tyre needed to be replaced. The table show the result of $$1000$$ cases :

    Distance in $$Km$$Frequency
    Less than $$4000$$       $$20$$
    $$4000$$ to $$9000$$      $$210$$
    $$9000$$ to $$14000$$      $$325$$
    More than $$14000$$      $$445$$

    If you buy a tyre of this company what is the probability that it will need to be replaced after it has covered somewhere between $$4000\, km$$ and $$14000\, km$$?

    Solution
    Probability that it will need to be replaced before it has covered $$ 4000 $$ km $$ = \dfrac {20}{1000} = 0.02 $$

    Probability that it will last more than $$ 9000 km  =  \dfrac { 325 + 445 } {1000} = \dfrac {770}{1000} = 0.77 $$

    Probability that it will need to be replaced after it has covered somewhere between $$ 4000 $$ km and $$ 14000 $$ km = $$ \dfrac { 210 + 325 } {1000} = \dfrac {535}{1000} = 0.535 $$

  • Question 5
    1 / -0
    A survey was conducted by car manufacturing company in a metropolitan city on $$1000$$ persons having monthly income from Rs. $$30,001$$ to Rs. $$50,000$$. The data about the number of persons in various categories is as under:

    Monthly income



    Number of Cars



    (in rupees)



    $$1$$



    $$2$$



    More than $$2$$



    $$30,001-40,000$$



    $$400$$



    $$50$$



    $$25$$



    $$40,001-50,000$$



    $$100$$



    $$300$$



    $$125$$


     Find the probability that a person selected at random in the income slab $$40,001-50,000$$ have more than $$2$$ cars.
    Solution
    A survey was conducted by car manufacturing company in a metropolitan city on $$1000$$ persons having monthly income from Rs. $$30,001$$ to Rs. $$50,000$$
    In the income slab $$40,001-50,000$$ having more than $$2$$ cars in the company is $$125$$ 
    Then 
     the probability that a person $$=\dfrac{125}{1000}=0.125$$

  • Question 6
    1 / -0
    A couple of dice rolled. What is the empirical probability of getting the sum as $$5$$?
    Solution
    Refer below diagram for sample space of two dice rolled to get sum of $$5$$

    When a pair of dice rolled possibilities for getting $$5$$ is $$(1, 4), (2, 3), (3, 2), (4, 1)$$

    Total number events occurred when we roll the dice $$= 36$$ 

    So, the empirical probability formula is as follows,

    $$P(E) =$$ $$\dfrac{4}{36}= \dfrac{1}{9}$$
  • Question 7
    1 / -0

    The record of a weather station shows that out of the past $$250$$ consecutive days, its weather forecasts were correct $$175$$ times. What is the probability that on a given day it was correct?

    Solution
    Total no. of days for which record of weather is given $$=250$$
    No. of days for which forecasts were correct $$= 175$$
       $$\therefore $$ favorable days $$= 175$$
       $$\therefore $$ probability $$= \displaystyle \frac {175}{250} = 0.7 $$

  • Question 8
    1 / -0
    A box has tokens numbered $$3$$ to $$100$$. If a token is taken out at random the chance that the number is divisible by $$7$$ is
    Solution
    The tokens are numbered from $$3$$ to $$100$$
    There are $$98$$ numbers from $$3$$ to $$100$$

    In this range the numbers divisible by $$7$$ are $$7, 14, 21, 28, 35, 42, 49, 56, 63, 70, 77, 84, 91$$ and $$98$$
    The number of numbers divisible by $$7$$ is $$14$$

    $$P$$(number divisible by $$7$$)$$=\displaystyle \frac{14}{98}=\frac{1}{7}$$

    Hence, the required probability is $$\dfrac{1}{7}$$
  • Question 9
    1 / -0
    You have a spinning wheel with 3 green sectors, 1 blue sector and 1 red sector,  if the probability of getting a non-blue sector is $$\dfrac{4}{m}$$. Then, the  value of $$m$$ is 

    Solution
    Out of 5 sectors, the pointer can stop at any of the sectors in 5 ways.

    $$\therefore $$ Total number of outcomes = $$5$$

     There are 4 non-blue sectors in the spinning wheel, out of which one can be obtained in 4 ways.

    So, the required probability = $$\dfrac{4}{5}$$

    Hence the value of $$m$$ is $$5$$
  • Question 10
    1 / -0
    A box contains $$32$$ coloured marbles. $$8$$ of them are red marbles and the rest are either blue or green marbles. A marble is drawn at random. Calculate the probability of drawing a marble which is not red in colour.
    Solution
     The marbles not in red color are $$32-8=24$$
    Then probability of not drawing red marbles is,
    $$P(E)=\dfrac{24}{32}\\\\\ \ \ \ \ \ \ \ =\dfrac{3}{4}$$
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