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The mean of the following distribution is 18 find the frequency f of class 19 to 21

Posted by Pooja Kumari 6 years, 6 months ago

CBSE > Class 10 > Mathematics

1 answers

Sia ? 6 years, 6 months ago

<th scope="col">Class interval</th> <th scope="col">Frequency f

11-13	3	12	36
13-15	6	14	84
15-17	9	16	144
17-19	13	18	234
19-21	f	20	20f
21-23	5	22	110
23-25	4	24	96
	{tex}\sum f _ { i } = 40 + f{/tex}		{tex}\sum f _ { i } x _ { i } = 704 + 20 f{/tex}

let the missing frequency is 'f'.
we know that , {tex}Mean= \frac { \sum f _ { i } x _ { i } } { \sum f _ { i } }{/tex}

{tex}\Rightarrow 18 = \frac { 704 + 20 f } { 40 + f }{/tex}
{tex}\Rightarrow 18(40 + f)=704 + 20f{/tex}
{tex}\Rightarrow 720 + 18f =704 + 20f{/tex}
{tex}\Rightarrow 2f = 16{/tex}
{tex}\Rightarrow{/tex} f = 8

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