$\sum_{i=1}^{10} (x_i - \bar{x}) = \dots$

In the formula $Z = l + \left( \frac{f_{1} - f_{0}}{2f_{1} - f_{0} - f_{2}} \right) \times c$ for the mode,$f_{0} = \ldots \ldots \ldots$

Find the mean of the following data by all the three methods:

Class	$50-70$	$70-90$	$90-110$	$110-130$	$130-150$	$150-170$
Frequency	$10$	$18$	$7$	$6$	$5$	$4$

The median class in the following frequency distribution is ..........

Class	$20-25$	$25-30$	$30-35$	$35-40$	$40-45$	$45-50$	$50-55$
Frequency	$2$	$5$	$8$	$10$	$7$	$10$	$3$

Find the median of the following frequency distribution:

Class	$0-10$	$10-20$	$20-30$	$30-40$	$40-50$	$50-60$	$60-70$	$70-80$
Frequency	$2$	$6$	$8$	$16$	$20$	$18$	$16$	$14$

The mileage $(km/l)$ of $50$ cars of the same model was tested by a manufacturer and details are tabulated as given below:

Mileage $(km/l)$	$10-12$	$12-14$	$14-16$	$16-18$
Number of cars	$7$	$12$	$18$	$13$

Find the mean mileage.
The manufacturer claimed that the mileage of the model was $16 \, km/l$. Do you agree with this claim?