Answer:
9 days
Explanation:
Given isabella saves a nickel a day.From this day onwards she kept on incresing the savings by doubling them.
Here it form's a geometric progression with first term(a) = 1 and common ratio (r) = 2
S(n) =

Given condition is S(n) >500


n ≥ 9
So it will take 9 days for her savings to be more than 500