Question

mercury from an illegally dumped hazardous waste container has been leaching into the river. an environmentalist tests a number of different sites along the river for levels of mercury and records her observations in the chart.

\

$$\begin{tabular}{|c|c|} \\hline \\text{sampling location} & \\text{mercury(ppb)} \\\\ \\hline 0 \\text{ km} & 300 \\\\ \\hline 1 \\text{ km downstream} & 30 \\\\ \\hline 2 \\text{ km downstream} & 3 \\\\ \\hline 3 \\text{ km downstream} & 0.3 \\\\ \\hline 4 \\text{ km downstream} & 0.03 \\\\ \\hline 5 \\text{ km downstream} & 0.003 \\\\ \\hline \\end{tabular}$$

how much more concentrated is the mercury concentration at its source than 4 kilometres downstream?

a) 300 times
b) 900 times
c) 1000 times
d) 10,000 times

Explanation:

Identify the concentration values

Using the Exponential Decay knowledge point

$$
LATEXBLOCK0
$$

Calculate the concentration ratio

Using the Exponential Decay knowledge point

$$
LATEXBLOCK1
$$

Answer:

• A) 300 times
• B) 900 times
• C) 1000 times
• D) 10,000 times (Correct answer)