Question

read the text. then answer the question.

molecules of nitrogen (n₂) and oxygen (o₂)
make up 99% of the gas particles in the
atmosphere. the remaining gases are present
at much smaller concentrations. measurements
made in 2015, for example, showed that carbon
dioxide (co₂) made up roughly 0.04% of the
gas particles in the atmosphere.

the amount of a particular gas in the
atmosphere can be expressed as a
concentration with units of parts per million,
or ppm. parts per million is a measurement of
the number of particles out of every million
particles. so, an atmospheric concentration of 1
ppm means that there is one particle of that
gas out of every million particles of gases in the
atmosphere. the atmospheric concentrations of
some gases are so small that they are
expressed in parts per billion or even parts per
trillion.

complete the statement.

one hundred years ago, the atmospheric concentration of carbon dioxide was about 300
ppm, or about 0.03% of the gas particles in the atmosphere. in 2015, the atmospheric
concentration of carbon dioxide was roughly ___ ppm.

300 350 400 450

Explanation:

Step1: Set up proportion

We know that \(0.03\%\) corresponds to \(300\) ppm. Let \(x\) be the ppm value for \(0.04\%\). Since the ratio of percentage to ppm is constant.
The proportion is \(\frac{0.03\%}{300}=\frac{0.04\%}{x}\)

Step2: Cross - multiply

Cross - multiplying gives \(0.03\%x = 0.04\%\times300\)
Since \(0.03\%=\frac{0.03}{100}\) and \(0.04\%=\frac{0.04}{100}\), the equation becomes \(\frac{0.03}{100}x=\frac{0.04}{100}\times300\)
Multiply both sides by \(100\) to get \(0.03x = 0.04\times300\)

Step3: Solve for \(x\)

First, calculate \(0.04\times300 = 12\). Then the equation is \(0.03x=12\).
Divide both sides by \(0.03\): \(x=\frac{12}{0.03}\)
\(x = 400\)

Answer:

\(400\)