The Environmental Protection Agency set a standard of 50 parts per billion of lead in drinking water. A new standard was set that safe water contains less than 15 parts per billion. a) write each of these rates as fractions using positive powers of ten. b) write each rate without fractions, using negative powers of ten.

a. 50/10^9.

15/10^9.

b. 50*10^-9
15*10^-9.