math problem
posted by tommy .
If I say I will give you a penny on the first day, 2 pennies on the second day, 4 pennies on the third day, and I just keep doubling and do this for a month, How much money would you have at the end of the month???

sum = 1+2+4+8+16+ ...
= 2^0 + 2^1 + 2^2 + 2^3 + ... 2^30
this is a geometric series
= a(r^n  1)/(r1)
= 2(2^30  1)/(21)
= 2 147 483 646 pennies
= $ 21 474 836.46
(check my arithmetic)