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 $$= \dfrac{9+11+14}{3}= 11\dfrac{1}{3}$$