I believe the complete
given is that the bucket of sand contains 9.5 billion grains of sand. That is:
bucket = 9,500,000,000
grains
and the concentration of
brown sand is 2 ppm:
concentration brown sand =
2 / 1,000,000
Therefore:
brown sand = 9,500,000,000
* (2 / 1,000,000)
brown sand = 19,000 grains
