In our day to day life, we can collect the following data.

1. Number of females per 1000 males in various states of our country

2. Weights of students of our class

3. Production of wheat in the last 10 years in our country

4. Number of plants in our locality

5. Rainfall in our city in the last 10 years

The information which is collected by the investigator himself with a definite objective in his mind is called as primary data
when the information is gathered from a source which already had the information stored, it is called as secondary data.
It can be observed that the data in 1, 3, and 5 is secondary data and the data in 2 and 4 is primary data.

The frequency means the number of students having same blood group.
It can be observed that 9 students have their blood group as A,
6 as B,
3 as AB, and
12 as O.

Therefore, the blood group of 30 students of the class can be represented as follows.

Blood group	Number of students
A	9
B	6
AB	3
O	12
Total	30

It can be observed clearly that 
Most common Blood Group (Highest frequency): O -(maximum number of students)
Rarest Blood Group (Lowest frequency): AB - (minimum number of students)

It is given that a grouped frequency distribution table of class size 5 has to be constructed. Therefore, the class intervals will be 0 - 5, 5 - 10, 10 - 15, 15 - 20…

By observing the data given as above, a grouped frequency distribution table can be constructed as follows.

Distance (in km)	Tally mark	Number of engineers
0 - 5		5
5 - 10		11
10 - 15		11
15 - 20		9
20 - 25		1
25 - 30		1
30 - 35		2
Total		40

It can be observed that there are very few engineers whose homes are at more than or equal to 20 km distance from their work place. Most of the engineers have their workplace up to 15 km distance from their homes.

(i) A grouped frequency distribution table of class size 2 has to be constructed. The class intervals will be 84 - 86, 86 - 88, and 88 - 90…

By observing the data given above, the required table can be constructed as follows.

Relative humidity (in %)	Number of days (frequency )
84 - 86	1
86 - 88	1
88 - 90	2
90 - 92	2
92 - 94	7
94 - 96	6
96 - 98	7
98 - 100	4
Total	30

(ii) It can be observed that the relative humidity is high. Therefore, the data is about a month of rainy season.

(iii) Range of data = Maximum value - Minimum value

= 99.2 - 84.9 = 14.3

(i) A grouped frequency distribution table has to be constructed taking class intervals 160 - 165, 165 - 170, etc. By observing the data given above, the required table can be constructed as follows.

Height (in cm)	Number of students (frequency )
150 - 155	12
155 - 160	9
160 - 165	14
165 - 170	10
170 - 175	5
Total	50

(ii) It can be concluded that more than 50% of the students are shorter than 165 cm.

Taking class intervals as 0.00, - 0.04, 0.04, - 0.08, and so on, a grouped frequency table can be constructed as follows.

Concentration of SO2 (in ppm)	Number of days (frequency )
0.00 - 0.04	4
0.04 - 0.08	9
0.08 - 0.12	9
0.12 - 0.16	2
0.16 - 0.20	4
0.20 - 0.24	2
Total	30

The number of days for which the concentration of SO₂ is more than 0.11 is the number of days for which the concentration is in between 0.12 - 0.16, 0.16 - 0.20, 0.20 - 0.24.

Required number of days = 2 + 4 + 2 = 8

Therefore, for 8 days, the concentration of SO₂ is more than 0.11 ppm.

By observing the data given above, the required frequency distribution table can be constructed as follows.

Number of heads	Number of times (frequency)
0	6
1	10
2	9
3	5
Total	30