Question

class11-13,13-15,15-17,17-19,19-21,21-23,23-25 and frequency is 3,6,9,13,f,5,4 Mean=18 find F​

Answer 1

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Answer 2

$\begin {tabular} {|c|c|c|c| }</p><p>\cline {1-4} class & frequency & class mark &f_{i}x_{i}\\</p><p>\cline {1-4} 11-13 &3&12&36 \\</p><p>\cline {1-4} 13-15&6&14&84 \\</p><p>\cline {1-4} 15-17&9&16&144 \\</p><p>\cline {1-4} 17-19&13&18&234\\</p><p>\cline {1-4} 19-21&f & 20& 20f \\</p><p>\cline {1-4} 21-23&5&22&110 \\</p><p>\cline {1-4} 23-25&4&24&96\\</p><p>\cline {1-4} -& \sum f_{i}=40+f &- &\sum f_{i}x_{i} = 704+20f \\</p><p>\cline {1-4}</p><p>\end {tabular}$

$Mean = 18 \: (given)$

$\red{ \frac{ \sum f_{i}x_{i} }{\sum f_{i} }} = 18$

$\implies \frac{704 + 20f}{40 + f } = 18$

$\implies 704 + 20f = 18( 40 + f )$

$\implies 704 + 20f = 720 + 18f$

$\implies 20f - 18f = 720 - 704$

$\implies 2f = 16$

$\implies f = \frac{16}{2}$

$\implies f = 8$

Therefore.,

$\red{ Value \: of \: f } \green {= 8 }$

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