The phrase "maintain an average" is correct and can be used in written English.
For example, you might say "I'm aiming to maintain an average of at least 90% in all my classes this semester."
The PMT voltage was adjusted to maintain an average ratio of 0.5 in untreated control.
The Passat was the only Volkswagen to maintain an average rating and to stay on the recommended list.
The student must maintain an average 3.0 grade point average (GPA) or better in both the depth area and overall.
The Citibank Account Package will waive A.T.M. fees when you maintain an average $10,000 monthly balance.
Mill Hill is adding a fifth kindergarten class next fall to maintain an average class size of 19, said the principal, Michael Rex Jones.
The student must maintain an average 3.0 grade point average (GPA) or better in both the depth area and overall courses taken.
The tolls are calculated every six minutes and change according to demand and traffic volume to maintain an average speed of 55 mph — the highway's posted speed limit.
The tolls are dynamic — meaning they change according to demand and volume of traffic to maintain an average vehicle speed of 55 mph.
Carefully controlled ventilation means that 85percentt of the time there is no need for air conditioning to maintain an average of 68 degrees.
By his calculations, the last week would need to maintain an average of 80 degrees to beat the record — a daunting task.
To maintain an average speed of 80.5 km/h on level ground requires 12 kW, equivalent to an energy density of 23 W h/kg.
