For a given frequency distribution,$\bar{x}=20, \Sigma f_{i} u_{i}=-50, n=100$ and $c=10$. Then,assumed mean $A = \ldots \ldots \ldots \ldots$

Find the mean of the following data:

Class	$200-299$	$300-399$	$400-499$	$500-599$	$600-699$	$700-799$	$800-899$
Frequency	$3$	$61$	$118$	$139$	$126$	$151$	$2$

Thirty women were examined in a hospital by a doctor and the number of heartbeats per minute were recorded and summarized as follows. Find the mean heartbeats per minute for these women,choosing a suitable method.

Number of heartbeats per minute	$65$-$68$	$68$-$71$	$71$-$74$	$74$-$77$	$77$-$80$	$80$-$83$	$83$-$86$
Number of women	$2$	$4$	$3$	$8$	$7$	$4$	$2$

While computing the mean of grouped data,we assume that the frequencies are

If the mean of $12, 13, x, 17, 18$ and $20$ is $16,$ then $x = \ldots \ldots \ldots \ldots .$

In a frequency distribution with total frequency $48$,$\bar{x}=70$,$\Sigma f_{i}=43+f$,and $A=66$. Then,the missing frequency $f=$ .........