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## Chapter 14: Statistics

#### TEXTBOOK’S EXERCISE – 14.2

5. A study was conducted to find out the concentration of sulphur dioxide in the air in parts per million (ppm) of a certain city. The data obtained for 30 days is as follows :

(i) Make a grouped frequency distribution table for this data with class intervals as 0.00 – 0.04, 0.04 – 0.08, and so on.

(ii) For how many days, was the concentration of sulphur dioxide more than 0.11 parts per million?

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

(ii) The concentration of sulphur dioxide was more than 0.11 ppm for 2 + 4 + 2 = 8 days.

6. Three coins were tossed 30 times simultaneously. Each time the number of heads occurring was noted down as follows :

7. The value of π up to 50 decimal places is given below :

3.14159265358979323846264338327950288419716939937510

(i) Make a frequency distribution of the digits from 0 to 9 after the decimal point.

(ii) What are the most and the least frequently occurring digits?

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

(ii) 3 and 9 occur most frequently while 0 occur least frequently.

8. Thirty children were asked about the number of hours they watched TV programmes in the previous week. The results were found as follows:

(ii) From the table, we see that only 2 children watched television for 15 or more than 15 hours a week.

9. A company manufactures car batteries of a particular type. The lives (in years) of 40 such batteries were recorded as follows:

Construct a grouped frequency distribution table for this data, using class intervals of size 0.5 starting from the interval 2 – 2.5.

Sol. The required grouped frequency distribution is given below:

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