Emissions of nitrogen oxides, which are major constituents of smog, can be modeled using a normal distribution. Let x denote the amount of this pollutant emitted by a randomly selected vehicle (in parts per billion). The distribution of x can be described by a normal distribution with µ = 1.6 and σ = 0.4. Suppose that the EPA wants to offer some sort of incentive to get the worst polluters off the road.
What emission levels constitute the worst 10% of the vehicles?