The number of observations in a group is 40. | vedclass

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(B) Let the sum of the first $10$ observations be $S_1$ and the sum of the remaining $30$ observations be $S_2$.Given that the average of the first $1

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$\frac{15}{4}$

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(B) Let the sum of the first $10$ observations be $S_1$ and the sum of the remaining $30$ observations be $S_2$.Given that the average of the first $10$ observations is $4.5$,we have:$S_1 = 10 	imes 4.5 = 45$Given that the average of the remaining $30$ observations is $3.5$,we have:$S_2 = 30 	imes 3.5 = 105$The total sum of all $40$ observations is $S = S_1 + S_2 = 45 + 105 = 150$.The average of the whole group is $\frac{S}{40} = \frac{150}{40} = \frac{15}{4}$.

Class	Frequency
$10-20$	$180$
$20-30$	$82$
$30-40$	$34$
$40-50$	$180$
$50-60$	$136$
$60-70$	$23$
$70-80$	$50$

The number of observations in a group is $40$. If the average of the first $10$ observations is $4.5$ and the average of the remaining $30$ observations is $3.5$,then the average of the whole group is:

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$10-20$ $180$
$20-30$ $82$
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$40-50$ $180$
$50-60$ $136$
$60-70$ $23$
$70-80$ $50$

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