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(D) The cumulative frequency of a class is the sum of the frequencies of all classes up to that class.Let $cf_n$ be the cumulative frequency of the $n

Vedclass · Accepted Answer

$15$

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(D) The cumulative frequency of a class is the sum of the frequencies of all classes up to that class.Let $cf_n$ be the cumulative frequency of the $n^{th}$ class and $f_n$ be the frequency of the $n^{th}$ class.We know that $cf_n = cf_{n-1} + f_n$.Therefore,$cf_{n-1} = cf_n - f_n$.Given that the cumulative frequency of the fourth class $(cf_4)$ is $25$ and the frequency of the fourth class $(f_4)$ is $10$,we have:$cf_3 = cf_4 - f_4$$cf_3 = 25 - 10 = 15$.Thus,the cumulative frequency of the third class is $15$.

Class	$0-20$	$20-40$	$40-60$	$60-80$	$80-100$
Frequency	$5$	$x$	$20$	$y$	$2$

Number of pages written per day	$16-18$	$19-21$	$22-24$	$25-27$	$28-30$
Number of days	$1$	$3$	$4$	$9$	$13$

For a given frequency distribution,the cumulative frequency of the fourth class is $25$ and the frequency of the fourth class is $10$. Then,the cumulative frequency of the third class is ...............

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Class $0-20$ $20-40$ $40-60$ $60-80$ $80-100$

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The following table gives the number of pages written by Sarika for completing her own book over $30$ days:

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