Find variance for following data:
Class $0 - 10$ $10 - 20$ $20 - 30$ $30 - 40$ $40 - 50$ $50 - 60$ $60 - 70$
frequency $6$ $5$ $8$ $15$ $7$ $6$ $3$

14.75

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15.75

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17.75

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16.75

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Solution

The correct option is C $16.75$
$¯ x = \frac{\sum F x}{\sum F} = \frac{1670}{50} = 33.4$
$σ^{2} = \frac{\sum F (x - ¯ x)^{2}}{\sum F} = \frac{14025.6}{50} = 280.51$
$σ = 16.75$

Suggest Corrections

Class	$0 - 10$	$10 - 20$	$20 - 30$	$30 - 40$	$40 - 50$	$50 - 60$	$60 - 70$
frequency	$6$	$5$	$8$	$15$	$7$	$6$	$3$

Class interval	$30 - 40$	$40 - 50$	$50 - 60$	$60 - 70$	$70 - 80$	$80 - 90$	$90 - 100$
Frequency	$3$	$7$	$12$	$15$	$8$	$3$	$2$

Marks	$10 - 20$	$20 - 30$	$30 - 40$	$40 - 50$	$50 - 60$	$60 - 70$	$70 - 80$
Frequency	$3$	$7$	$10$	$6$	$8$	$2$	$4$

Class	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