Question

A board is made up of 9 squares. A certain number of pennies is placed in each

square, following a geometric sequence. The first square has 1 penny, the second
has 2 pennies, the third has 4 pennies, etc. When every square is filled, how many
pennies will be used in total?
A
512
B
511
256
D
81

Answer 1

B) 511

Explanation:

1. How many pennies are in the last square:

Sequence: # of pennies = 2^(box # - 1)

Plug in: # = 2⁸

Solve: # of pennies in box 9 = 256

2. Process of elimination:

Not C or D, since the total must be greater than 256.

So the answer is B, not A, since 2⁰ + 2¹ ... 2⁷ = 2⁸ + 1.