Answer:
Step-by-step explanation:
Given AP with:
- a₁= 28, aₙ = 79, Sₙ = 963
Use the formula:
- Sₙ = 1/2n(a₁ + aₙ), sum of the first n terms
Substitute given values and solve for n:
- 963 = 1/2n(28 + 79)
- 963 = 1/2n(107)
- 1/2n = 963/107
- 1/2n = 9
- n = 9*2
- n = 18
