Question

Jill arranges quarters in stacks of increasing powers of 2, starting with the zeroth power (20). If she ends up with six stacks, how many coins has she used?

Answer 1

Stack 1 : 2^0 = 1 quarter.
Stack 2 : 2^1 = 2 quarters.
Stack 3: 2^2 = 4 quarters.
Stack 4: 2^3 = 8 quarters.
Stack 5 : 2^4 = 16 quarters.
Stack 6: 2^5 = 32 quarters.
1 + 2 + 4 + 8 + 16 + 32 = 63
Answer: She used 63 quarters.