Geof the Giraffe

Question

Geoff the Giraffe walked 117miles, beginning on Sunday morning and finishing on Monday evening of the following week.  Each day, he walked 1 mile farther than the day before.  How many miles did Geoff walk each day?

Answer 1

S9 = (n/2)(2a1 + (n - 1)d)
117 = (9/2)(2a1 + 8)
234 = 9(2a1 + 8)
26 = 2a1 + 8
18 = 2a1
9 = a1

9, 10, 11, .......