If you save one penny on january 1 two pennies on january 2 and three on january 3 and continue this pattern for a year. how many pennies will you have

The formula you need is: S = (n/2) (2a1 + (n - 1) x d)
so then you plug in the numbers:
S = (365/2) (2 x 1 + (365 - 1) x 1)
then combine like terms:
S = 66795 pennies
A dollar is 100 pennies. Therefore, at the end of the year, the total savings is $667.95.