Questions

Strength of concrete increases with increase in water cement ratio as the strength of the cement is directly proportional to water cement ratio.

Tractor was the single most important invention to farmers.

The lightest computer is the tablet.

Teens drinking are at risk of date rape, becoming an alcoholic, HIV and other STDs.

Resistivity :

Resistivity is a measure of the resistance to the flow of electrons. 

Conductivity :

Conductivity is just the inverse of resistivity, σ = 1/ρ, where σ is conductivity and ρ is resistivity.

Example:

Think of a pipe and water, the bigger the pipe, the easier water can flow and thus the lower the resistance. 

The main excretory organs of insects and spiders are Malpighian tubules.