-
Question 1: The relationship between mean, median and mode for a moderately skewed distribution is:
Solution: (A) Mode = 3 Median - 2 Mean
Reason: This is the empirical relationship between the three measures of central tendency. -
Question 2: Construction of a cumulative frequency table is useful in determining the:
Solution: (B) Median
Reason: Cumulative frequencies are specifically used to find the median class and calculate the median. -
Question 3: In the formula $\bar{x} = a + \frac{\sum f_i d_i}{\sum f_i}$ for finding the mean of grouped data, $d_i$'s are deviations from $a$ of:
Solution: (C) mid-points of the classes
Reason: $d_i = x_i - a$, where $x_i$ are the class marks (mid-points). -
Question 4: If the arithmetic mean of $x, x+3, x+6, x+9$ and $x+12$ is 10, then $x$ is equal to:
Solution: (D) 4
Step 1: Sum $= 5x + 30$. Number of terms $= 5$.
Step 2: Mean $= \frac{5x+30}{5} = x+6$.
Step 3: $x+6 = 10 \Rightarrow x = 4$. -
Question 5: While computing mean of grouped data, we assume that the frequencies are:
Solution: (B) centred at the classmarks of the classes
Reason: We use the class mark $x_i$ to represent the entire class interval. -
Question 6: If $x_i$'s are the mid-points of the class intervals of grouped data, $f_i$'s are the corresponding frequencies and $\bar{x}$ is the mean, then $\sum (f_i x_i - \bar{x})$ is equal to:
Solution: (A) 0
Step 1: $\sum (f_i x_i - \bar{x})$ is not standard notation, usually it implies $\sum f_i(x_i - \bar{x})$.
Step 2: $\sum (f_i x_i - f_i \bar{x}) = \sum f_i x_i - \bar{x} \sum f_i = N\bar{x} - \bar{x}(N) = 0$. -
Question 7: For the following distribution:
The sum of lower limits of the median class and modal class is:Class 0-5 5-10 10-15 15-20 20-25 Frequency 10 15 12 20 9 Solution: (B) 25
Step 1: Modal class is 15-20 (max freq 20). Lower limit = 15.
Step 2: Total freq $N = 10+15+12+20+9 = 66$. $N/2 = 33$.
Step 3: CF: 10, 25, 37... 33 lies in 10-15. Median class is 10-15. Lower limit = 10.
Step 4: Sum $= 15 + 10 = 25$. -
Question 8: Consider the following frequency distribution:
The upper limit of the median class is:Class 0-5 6-11 12-17 18-23 24-29 Frequency 13 10 15 8 11 Solution: (B) 17.5
Step 1: Classes are discontinuous. Convert to continuous: 0.5-5.5, 5.5-11.5, 11.5-17.5...
Step 2: $N = 13+10+15+8+11 = 57$. $N/2 = 28.5$.
Step 3: CF: 13, 23, 38. 28.5 lies in 12-17 (continuous 11.5-17.5).
Step 4: Upper limit is 17.5. -
Question 9: The mean of first $n$ odd natural numbers is:
Solution: (C) $n$
Step 1: Sum of first $n$ odd numbers is $n^2$.
Step 2: Mean $= \frac{\text{Sum}}{n} = \frac{n^2}{n} = n$. -
Question 10: If the mode of a distribution is 8 and its mean is 8, then its median is:
Solution: (C) 8
Step 1: 3 Median = Mode + 2 Mean.
Step 2: 3 Median $= 8 + 2(8) = 24$.
Step 3: Median $= 24/3 = 8$.