A survey asks 40 students how many hours they play video games in a week…

Step 1. The mean. The last class has no upper end, so it has no class mark. The mean cannot be found.

Step 2. The median. The cumulative frequencies are $8, 23, 35, 39, 40$, and $\dfrac{N}{2} = 20$. The median class is $5$ to $10$, with $cf = 8$ and $f = 15$. Then $\text{median} = 5 + \dfrac{20 - 8}{15} \times 5 = 5 + 4 = 9$ hours.

Step 3. The mode. The modal class is $5$ to $10$, with $f_1 = 15$, $f_0 = 8$ and $f_2 = 12$. Then $\text{mode} = 5 + \dfrac{15 - 8}{30 - 8 - 12} \times 5 = 5 + 3.5 = 8.5$ hours.

What do you notice? The one student in the open class does not change the median or the mode, however many hours that student plays. That is why the median is a good average for data with an open last class.