Answer:
34
Step-by-step explanation:
Since the pennies need to be kept under the pillow in order to be doubled, we're really looking for the day the girl will wake up with 5 billion pennies under her pillow.
The general formula of that geometric sequence will be: t = 1 + 2^(n-1)
We need to find the value of n when t will be over 5,000,000,000.
So, the equation becomes:
5,000,000,001 = 1 + 2^(n-1)
(n-1) * log(2) = log(5,000,000,000)
n-1 = log(5,000,000,000) / log(2)
n-1 = 22.25
n = 33.25
Since it has to be complete days, and we have to reach over 5 billion, then we round it up to 34.