Question

The sum of the first four terms of an arithmetic progression is 56. The sum of the last four terms is 112. If its first term is 11, then the number of terms is:

• A. 10
• B. 11
• C. 12
• D. 13

Hint:

For problems involving the sum of specific terms in an arithmetic progression, use the general sum formula for arithmetic progressions: \[ S_n = \frac{n}{2} \times (2a + (n-1)d) \] Also, remember that the sum of consecutive terms is another way to work with the properties of an arithmetic progression.