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## Chapter 14: Statistics

#### TEXTBOOK’S EXERCISE – 14.1

1. Give five examples of data that you can collect from your day-to-day life.

Sol. (i) A number of children each family have in our building.

(ii) Marks obtained by each student of our class in maths in the half-yearly examination.

(iii) A number of people living in our colony who are below 18 years.

(iv) Water bills of our house for the last three years.

(v) Heights of 30 plants around your colony.

2. Classify the data in Q.1 above as primary or secondary data.

Sol. All are primary data

TEXTBOOK’S EXERCISE – 14.2

1. The blood groups of 30 students of Class VIII are recorded as follows :

A, B, O, O, AB, O, A, O, B, A, O, B, A, O, O,

A, AB, O, A, A, O, O, AB, B, A, O, B, A, B, O.

Represent this data in the form of a frequency distribution table. Which is the most common, and which is the rarest, blood group among these students?

Sol. We can represent the above data as follows.

From the table, we have, most common blood group is O. Rarest blood group is AB.

 Blood group No. of students A 9 B 6 O 12 AB 3 Total 30

2. The distance (in km) of 40 engineers from their residence to their place of work was found as follows:

Construct a grouped frequency distribution table with class size 5 for the data given above taking the first interval as 0-5 (5 not included). What main features do you observe from this tabular representation?

Sol. We can represent the above data in a grouped frequency distribution table as below:

From the table, we observe that 5 + 11 + 11 + 9 = 36 engineers live at a distance of 20 km from their workplace. Only 4 engineers live at a distance of 20 km or more from their workplace.

3. The relative humidity (in %) of a certain city for a month of 30 days was as follows :

(i) Construct a grouped frequency distribution table with classes 84 – 86, 86 – 88, etc.

(ii) Which month or season do you think this data is about?

(iii) What is the range of this data?

Sol. (i) The required frequency distribution table is shown below.

(ii) From the table, we see that the relative humidity is high, so the data is of the rainy season.

(iii) Highest score = 99.2

Lowest score = 84.9

So, the range of the data

= 99.2 – 84.9 = 14.3

4. The heights of 50 students, measured to the nearest centimetres, have been found to be as follows:

(i) Represent the data given above by a grouped frequency distribution table, taking the class intervals as 160 – 165, 165 – 170 etc.

(ii) What can you conclude about their heights from the table?

Sol. (i) The required frequency distribution table is shown below:

(ii) From the table, we see that 12 + 9 = 21 students are shorter than 160 cm. Remaining 29 students are taller than or equal to 160 cm.