Cumulative Frequency
1. We are given the frequency table for length intervals and need to find the missing cumulative frequency table values $A$, $B$, and $C$.
2. Cumulative frequency is the running total of frequencies up to the upper boundary of the interval.
3. From the first table, the frequencies for intervals are:
- $4 < x \leq 8$: 4
- $8 < x \leq 12$: 15
- $12 < x \leq 16$: 7
- $16 < x \leq 20$: 4
4. The cumulative frequencies are calculated by adding frequencies up to that point:
- For $4 < x \leq 8$: cumulative frequency is 4 (given)
- For $4 < x \leq 12$: cumulative frequency is $4 + 15 = 19$ (given)
5. For the interval $A < x \leq B$: cumulative frequency $C$ corresponds to the next cumulative frequency after $4 < x \leq 12$, which covers the interval $12 < x \leq 16$.
6. Calculate cumulative frequency for $12 < x \leq 16$ (which gives $C$):
$$
C = 19 + 7 = 26
$$
7. The lower limit $A$ of this interval is 12, the upper limit $B$ is 16.
8. Finally, verify cumulative frequency for $4 < x \leq 20$:
$$
4 + 15 + 7 + 4 = 30
$$
Which matches the given total.
**Answer:**
- $A = 12$
- $B = 16$
- $C = 26$