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Statistics Test - 29

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Statistics Test - 29
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  • Question 1
    1 / -0
    The blood groups of 30 students are recorded as follows:
    $$A, B, O, A, AB, O, A, O, B, A, O, B, A, AB, B, A,$$
    $$ AB, B, A, A, O, A, AB, B, A, O, B, A, B, A$$
    What are the frequency distribution for the data $$A$$ and $$AB$$ ?
    Solution
    Frequency is the number of times the data has occured in the data set.

    The frequency of the data $$A$$ is $$12$$. Since, $$A$$ has occured $$12$$ times in the given data set.

    Similarly $$AB$$ has occured $$4$$ times in the data set. Therefore the frequency of $$AB$$ is $$4$$
  • Question 2
    1 / -0
    In the class intervals $$10-20, 20-30$$, the number $$20$$ is included in:
    Solution
    The number is always included in the lower limit of the class interval. Hence, $$20$$ is included in $$20-30$$
  • Question 3
    1 / -0
    Let $$m$$ be the mid-point and $$l$$ be the upper class limit of a class in a continuous frequency distribution. The lower class limit of the class is:
    Solution
    Let $$a$$ be lower class limit, $$l$$ is the upper class limit and $$m$$ is the mid-point
    then, mid-point $$m = \dfrac{a +l}{2}$$ 
    Therefore, $$a = 2m - l$$
  • Question 4
    1 / -0
    In a frequency distribution, the mid value of a class is $$10$$ and the width of the class is $$6$$. The lower limit of the class is:
    Solution


    $$\textbf{Step1: Find the values}$$
                  $$\text{Let $$x$$ and $$y$$ be the upper and lower class limit in a frequency distribution.}$$ 
                   $$\text{Given, mid value of a class is 10}$$
                   $$\Rightarrow \dfrac{x+y}{2}=10$$
                   $$\Rightarrow x+y=20 \ldots (1)$$
                   $$\text{Also given that, width of the class is 6}$$ 
                   $$x-y=6 \ldots(2)$$
                   $$\text{On Adding equation $$(1)$$ and $$(2)$$, we get}$$
                   $$\Rightarrow 2 x=20+6 $$
                   $$\Rightarrow 2 x=26 $$
                   $$\Rightarrow x=13 $$
                   $$\text{On putting $$x=13$$ in (1) we get}$$
                   $$\Rightarrow 13+y=20 $$
                   $$\Rightarrow y=7 $$
     $$\textbf{Hence the lower limit of the class is $$7$$.}$$
  • Question 5
    1 / -0
    A grouped frequency table with class intervals of equal sizes using $$250-270$$ ($$270$$ not included in this interval) as one of the class interval is constructed for the following data :
    $$268, 220, 368, 258, 242, 310, 272, 342,$$
    $$310, 290, 300, 320, 319, 304, 402, 318,$$
    $$406, 292, 354, 278, 210, 240, 330, 316,$$
    $$406, 215, 258, 236.$$
    The frequency of the class $$310-330$$ is:
    Solution
    Numbers between $$310$$ and $$330$$ are $$310, 310, 320, 319, 318, 316.
     \space 330$$ will not be included in this interval. Thus, frequency is $$6$$.
  • Question 6
    1 / -0
    To draw a histogram to represent the following frequency distribution:
    Class Interval 
    $$5-10$$
    $$10-15$$
    $$15-25$$
    $$25-45$$
    $$45-75$$
    Frequency
    $$6$$
    $$12$$
    $$10$$
    $$8$$
    $$15$$
    The adjusted frequency for the class $$25-45$$ is:
    Solution
    The frequency distribution will consist of classes with an interval of $$5$$. The class $$25-45$$ includes four such classes with an interval of $$5$$. Thus the adjusted frequency will be $$\dfrac{8}{4}=2$$
  • Question 7
    1 / -0
    A grouped frequency distribution table with classes of equal sizes using $$63-72$$ $$(72$$ included$$)$$ as one of the class is constructed for the following data:
    $$30, 32, 45, 54, 74, 78, 108, 112, 66, 76, 88,\\
    40, 14, 20, 15, 35, 44, 66, 75, 84, 95, 96,\\
    102, 110, 88, 74, 112, 14, 34, 44$$
    The number of classes in the distribution will be:
    Solution
    If one the classes is $$63-72$$ then the range of the class is $$10$$  $$(72$$ included$$)$$
    Range of the given data points $$= 112-30 = 82$$

    Number of classes $$= \dfrac{82}{10} = 8.2$$
    Classes required will be $$9$$ after round off.
  • Question 8
    1 / -0
    The width of each of five continuous classes in a frequency distribution is $$5$$ and the lower class-limit of the lowest class is $$10$$. The upper class-limit of the highest class is:
    Solution
    Lower class limit $$= 10$$
    Width of each class $$= 5$$
    Width till the upper class limit for a frequency distribution having $$5$$ classes $$= 5\times 5=25$$ 

    Hence, the upper class limit of highest class $$= 10 +25 =35$$
  • Question 9
    1 / -0
    The class marks of a frequency distribution are given as follows: $$15, 20, 25, ...$$
    The class corresponding to the class mark $$20$$ is:
    Solution
    Class marks are: $$15, 20, 25, ...$$

    Lower limit of class $$20$$ is mean of $$15$$ and $$20 = \cfrac{15+20}{2} = 17.5$$
    Upper limit of class $$20$$ is the mean of $$20$$ and $$25= \cfrac{20+25}{2} = 22.5 $$

    $$20$$ is the class mark for the class interval $$17.5-22.5$$
  • Question 10
    1 / -0
    If the mean of the observations:
    $$x, x + 3, x + 5, x + 7, x + 10$$ is $$9$$, the mean of the last three observations is
    Solution
    Mean of $$x, x + 3, x + 5, x + 7, x + 10 = 9$$
    Sum of the terms $$= 5x + 25$$
    Mean = $$\dfrac{5x+25}{5} =9$$
    $$x +5 =9$$
    $$x =4$$
    Last three observations are $$9,11,14$$
    Mean $$= \dfrac{9+11+14}{3}= 11\dfrac{1}{3}$$
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