Geometric Sequences

Question

An 18 story building is being constructed so that the 1st floor is 22150. square feet, the 2nd floor is 18827.5 square feet, the 3rd floor is 16003.4 square feet, and so on. How large, in square feet, is the top floor. I can do this problem the long way and I'm terrible with coming up with equations. What is an equation that can help me solve this quickly?

Answer 1

22150, 18827.5, 16003.375,... is a geometric sequence with common ratio r = 0.85

 

Area of 18th floor = a₁r¹⁷  ≈ 1397.96 ft²