In the formula $\bar{x} = A + \frac{\Sigma f_{i} u_{i}}{\Sigma f_{i}} \times c$,$c$ represents .......

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

$Z - M = \ldots \ldots \ldots \times (M - \bar{x})$

The mean of the following frequency distribution is $43.75$. Find the missing frequency $f$.

Class	$0-10$	$10-20$	$20-30$	$30-40$	$40-50$	$50-60$	$60-70$	$70-80$	$80-90$	$90-100$
Frequency	$8$	$4$	$20$	$45$	$64$	$32$	$f$	$8$	$2$	$2$

Calculate the mean of the following frequency distribution:

Class	$10-20$	$20-30$	$30-40$	$40-50$	$50-60$
Frequency	$12$	$16$	$8$	$6$	$8$

The times,in seconds,taken by $150$ athletes to run a $110\, m$ hurdle race are tabulated below:

Class (seconds)	$13.8-14.0$	$14.0-14.2$	$14.2-14.4$	$14.4-14.6$	$14.6-14.8$	$14.8-15.0$
Frequency	$2$	$4$	$5$	$71$	$48$	$20$

The number of athletes who completed the race in less than $14.6\, s$ is: