Question

Jim opens a savings account with $5. His account doubles every month. How much will he have after the 8th month?
1st 2x5=10
2nd 10x2=20
3rd 20x2=40
4th 40x2=80
5th 80x2=160
6th 160x2=320
7th 320x2=640
8th 640x2=1280

1280 was marked wrong. why?

Answer 1

According to the wording of the question, your answer is correct

Now -- 5
at end of month 1 = 5(2) = 10
at end of month 2 = 5(2^2) = 5(4) = 20
at end of month 3 = 5(2^3) = 5(8) = 40
...
at end of month 8 = 5(2^8) = 5(256) = 1280