A drop of water contains about 40 billion molecules If a buc

A drop of water contains about 40 billion molecules.  If a
    bucket has half a million drops of water in it, how many molecules of water are in the
    bucket? Write your answer in scientific notation.

Solution

1 drop contains 40 billion molecules that is 40x10^9

half million drop means 0.5x10^6 drops

so total number of molecules in bucket=40x10^9 x 0.5x10^6=20x10^15

or 2x10^16 molecules