Find the mean for the following distribution
Marks 10-20 20-30 30-40 40-50 50-60 60-70 70-80
Frequency 6 8 13 7 3 2 1

30

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35.75

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25

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28

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Solution

The correct option is B $35.75$
Answer:- $x_{i} = \frac{Upper limit + Lower limit}{2}$

Marks Frequency $x_{i}$ $x_{i} . f_{i}$
10-20 6 15 90
20-30 8 25 200
30-40 13 35 455
40-50 7 45 315
50-60 3 55 165
60-70 2 65 130
70-80 1 75 75
$Σ f_{i} = 40$ $Σ x_{i} . f_{i} = 1430$
Mean = $\frac{Σ x_{i} . f_{i}}{Σ f_{i}} = \frac{1430}{40} = 35.75$

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Similar questions

Class	10-20	20-30	30-40	40-50	50-60	60-70	70-80
Frequency	3	6	8	10	8	5	3

Class	10-20	20-30	30-40	40-50	50-60	60-70	70-80	80-90
Frequency	9	11	15	24	19	9	8	5

C.I.	0-10	10-20	20-30	30-40	40-50	50-60	60-70	70-80
Freq.	5	8	7	12	28	20	10	10

Class-interval:	0-10	10-20	20-30	30-40	40-50	50-60	60-70	70-80
Frequency:	$5$	$8$	$7$	$12$	$28$	$20$	$10$	$10$

Class-interval:	10-15	15-20	20-25	25-30	30-35	35-40
Frequency:	$30$	$45$	$75$	$35$	$25$	$15$

Class-interval:	25-30	30-35	35-40	40-45	45-50	50-60
Frequency:	$25$	$34$	$50$	$42$	$38$	$14$

Class Interval	0 - 10	10 - 20	20 - 30	30 - 40	40 - 50	50 - 60	60 - 70	70 - 80
Frequency	7	14	13	12	20	11	15	8

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