Amixture of pulverized fuel ash and portland cement to be used for grouting should have a compressive strength of more than 1300 kn/m2. the mixture will not be used unless experimental evidence indicates conclusively that the strength specification has been met. suppose compressive strength for specimens of this mixture is normally distributed with σ = 64. let μ denote the true average compressive strength.

the aurora is formed when charged particles emitted from the sun during a solar flare penetrate the earth's magnetic shield and collide with atoms and molecules in our atmosphere. these collisions result in countless little bursts of light, called photons, which make up the aurora.

auroras are generated by charged solar particles hitting molecules in earth's atmosphere. this usually happens in high latitudes, because our planet’s magnetic field tends to funnel these particles toward the poles. that’s why it can be experienced in northern ohio.