Find the mean of the following distribution.

Class	Frequency
$0-20$	$5$
$20-40$	$8$
$40-60$	$10$
$60-80$	$12$
$80-100$	$7$
$100-120$	$8$

Class frequency(f) Class mark(x) fx

0-20 5 10 50

20-40 8 30 240

40-60 10 50 500

60-80 12 70 840

80-100 7 90 630

100-12 8 110 880

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50 3140

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Then, mean $=\frac{3140}{50}=62.8$