The phrase "a number of grades" is correct and usable in written English.
It can be used when referring to multiple grades or levels, often in an educational context.
Example: "The students received a number of grades for their performance throughout the semester."
Alternatives: "several grades" or "various grades".
There are a number of grades of sheet steel and these comprise by far the greatest part of the soft, high-permeability material used.
The creep characteristics of drawn samples of a number of grades of polyethylene have been studied over a range of applied stresses and strains.
Futures markets, on the other hand, generally permit trading in a number of grades of the commodity to protect hedger sellers from being "cornered" by speculator buyers who might otherwise insist on delivery of a particular grade whose stocks are small.
He has a student who has taken a number of grade exams, but can't "swing" a piece, jazz-style.
They include the Grade I listed Barningham Hall, which is of Jacobean origin; Baconsthorpe Castle, also Grade I, and a number of Grade II* churches.
Van Dyke is his fifth jockey so far, and while Term of Art has taken his shots in a number of Grade 1 races, he's never finished better than seventh.
A number of grading systems have been used to report oxaliplatin-associated neurotoxicity.
An animal may be regarded as fully kindled after manifesting a number of grade 5 seizures.
A number of grading systems exist, including the Silverberg 6, the International Federation of Gynecology and Obstetrics (FIGO) 7, the World Health Organization (WHO) 8, and the Gynecologic Oncology Group (GOG) systems 9.
The authors also reported a number of grade 3 and 4 cardiopulmonary adverse events, including hypertension in eight patients (20%)— also seen in PX-171-007 as PX-171-007 asnary edema/congestive heart failure (CHF) in four patients (10%) and left ventricular systolic dysfunction in twellasents (5%).
