
Per
Quantifying Costs
Use 'per' to talk about prices in relation to a unit of measure.
Gasoline is sold per litre.
Rate Frequency
Use 'per' to specify the frequency of an occurrence within a time period.
She goes to the gym five times per week.
Statistical Figures
Use 'per' when providing statistical information, such as ratios or averages.
There are 35 students per teacher in this school.