Answer:
250,000 to 700,000 parts
Step-by-step explanation:
For the lower ratio of 0.5, we have to get 0.5 flouride parts/1 gallon of water equivalent to (some fluoride parts)/ (500,000 gallons of water). we can multiply 500,000 by 0.5 to get 250,000 as our lower limit. Similarly, we can multiply 500,000 by 1.4 to get 700,000 as our upper limit
