A factory is polluting a river such that at every mile down river from the factory an environmental expert finds 15% less pollutant than at the preceding mile.If the pollutant's concentration is 600 ppm (parts per million)at the factory,what is its concentration 12 miles down river?
A) 180 ppm
B) 90 ppm
C) 85.35 ppm
D) 705.88 ppm
E) 100.41 ppm

Question

A factory is polluting a river such that at every mile down river from the factory an environmental expert finds 15% less pollutant than at the preceding mile.If the pollutant's concentration is 600 ppm (parts per million)at the factory,what is its concentration 12 miles down river? ​
A) 180 ppm
B) ​90 ppm
C) ​85.35 ppm
D) 705.88 ppm
E) ​100.41 ppm

Quizplus · Accepted Answer

We can use the formula:

concentration at a certain mile = initial concentration * (1 - % decrease)^number of miles

For 12 miles down river, we have:

concentration at 12th mile = 600 ppm * (1 - 0.15)^12 
concentration at 12th mile = 85.35 ppm

Therefore, the answer is C.

A Factory Is Polluting a River Such That at Every