Question

I need help solving this problem

Answer 1

The exact number of grains of rice would exceed all of the rice ever grown from the dawn of mankind. The promise could not be kept.

Answer 2

This is a geometric sum which has the form:

s(n)=a(1-r^n)/(1-r), a=initial term, r=common ratio, n=term number...

In this case a=1 and r=2 so

s(n)=(1-2^n)/(1-2)

s(n)=-(1-2^n)

There are 8*8=64 squares so:

s(64)=-(1-2^64)

s(64)=18,446,744,073,709,551,615  grains of sand...

that's over 18 quintillion grains of sand :P that is roughly the same amount of grains of sand on the entire earth...