A factory is polluting a river such that at every mile down river from the factory an environmental expert finds 20% less pollutant than at the preceding mile. If the pollutant's concentration is 700 ppm (parts per million) at the factory, what is its concentration 15 miles down river?
A)140.00 ppm
B)300.00 ppm
C)24.63 ppm
D)875.00 ppm
E)30.79 ppm

Question

Quizplus · Accepted Answer

For every mile down river, the pollutant concentration decreases by 20%. Thus, the concentration 15 miles down river can be found by multiplying the initial concentration of 700 ppm by 0.8 fifteen times (since the concentration decreases by 20% 15 times).

700 * 0.8^15 = 24.63 ppm

Therefore, the pollutant concentration 15 miles down river is 24.63 ppm.

A Factory Is Polluting a River Such That at Every