Arsenic is toxic to humans. The greatest amount of arsenic that is allowed in drinking water is 10 parts per billion. A test shows that a source of drinking water contains 0.000002% arsenic. Is this an allowable amount? Explain.

The decimal you put would be "two ten-millionths" if read out loud. If the allowable amount is 10 parts per billion, it would be 1 part per 100 million. Because 2 parts per 10 million is also 20 parts per 100 million, it is not not an acceptable amount