Algebra-1

Question Analysis
This question involves grouping intervals into "middle" and "outer" categories, summing their frequencies, and finding the difference between the two sums.
The main focus is on categorizing intervals, calculating two total frequencies, and performing subtraction.

Key Concept Explanation
Grouped Frequency Differences: When intervals are ordered, "middle intervals" are the two in the center, and "outer intervals" are the first and last. The difference is calculated by subtracting the sum of outer frequencies from the sum of middle frequencies.

Step-by-Step Solution
Identify middle and outer intervals:
Middle intervals: 7–9 and 10–12 (second and third intervals in order).
Outer intervals: 4–6 and 13–15 (first and fourth intervals).