EXERCISE 28 A

1.Write (T) for true or (F) for false. Use the following frequency table.

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<tr><th>Age</th><td>13</td><td>14</td><td>15</td><td>16</td><td>17</td><td>18</td><td>19</td></tr>

<tr><th>Frequency</th><td>3</td><td>2</td><td>7</td><td>2</td><td>3</td><td>2</td><td>1</td></tr>

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(i) The frequency of 19 is 1

(ii) The frequency of 14 is 3

(iii) 17 has the lowest frequency

(iv) 16 has a frequency of 2

(v) 15 has the highest frequency

(vi) The frequency of 13 is 3

2.The ages of all the workers in a certain company are as follows:

23,28,25,21,40,50,50,21,40,50,33,23,41,25,33,37,23,26,41,37,37,21,43,33,37,23,32,33,43,32.

(i) Construct a frequency table for the above data.

(ii) How many workers are over 35 years old ?

(iii) How many workers are under 30 years old ?

(iv) What is the least age?

3.Find the mean of the following sets of numbers.

(i)2.5,2.4,3.5,2.8,2.9,3.3,3.6

(ii)-6,-2,-1,0,1,2,5,9

4.Anu received 85, 73, 92, 61 and 89 marks in five tests. What are her mean marks?

5.Priya practiced on her sitar 45 minutes, 30 minutes, 60 minutes, 50 minutes and 20 minutes. What was her mean practice time ?

6.Find the mean of the first ten prime numbers.

7.Shikha secured 73, 86, 78 and 75 marks in four tests. What is the least number of points she can secure in her next test if she is to have an average of 80?

8.The mean of 5 numbers is 20. if one number is excluded, mean of the remaining numbers becomes 23.Find the excluded number.

9.Find the mean of the following distributions

(i)<div style=”overflow: auto;”>

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<tr><th>x</th><td>4</td><td>6</td><td>9</td><td>10</td><td>15</td></tr>

<tr><th>f</th><td>5</td><td>10</td><td>10</td><td>7</td><td>8</td></tr>

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(ii)<div style=”overflow: auto;”>

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<tr><th>x</th><td>10</td><td>30</td><td>50</td><td>70</td><td>89</td></tr>

<tr><th>f</th><td>7</td><td>8</td><td>10</td><td>15</td><td>10</td></tr>

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10.The following table gives the height in cm and the number of plants of each height. Compute the mean height of the plants.

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<table>

<tr><th>Height in cm (x)</th><td>50</td><td>53</td><td>61</td><td>64</td><td>67</td><td>70</td></tr>

<tr><th>Number of plants (f)</th><td>15</td><td>10</td><td>18</td><td>12</td><td>25</td><td>20</td></tr>

</table>

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