Geometric and arithmetic algebra

Question

mandy a skill biker is preparing to ride her bike in an upcoming race she will ride her bike for 15 miles the first week, and each week following, she will ride 4% more than the previous week. Using a geometric series formula find the total number of miles Mandy will ride her bike during the first 8 week of training.

Answer 1

A1 = 15

A2 = 15(1.04)A3 = 15(1.04)^2

...

AN = 15(1.04)^(N-1)

...

A8 = 15(1.04)^7

S8 = A1+A2+ A3 + ...AN ...+ A8 = 138.2133939

SN=A1(1-r^N)/(1-r) with r = 1.08

S8 = 15(1-(1.04)^8/(1-1.04) = 138.2133939

sum of the first 8 = 138.2133929

Answer 2

S₈ = 15(1.04⁸ - 1) / (1.04 - 1)

Can you calculate and answer?