I don't know if anyone actually collects statistics on this, but I suspect the real answer is "considerably more than deserve a grade of C or above."
Assuming the teacher grades on a (real, bell) curve and sets the grade divisions based on standard deviations (within 0.5 SD of the mean = C, 0.5 over to 1.5 over = B, more than 1.5 SDs over = A) then about 69 percent will get C or above, around 24% will get a D, and 6.7% will fail (38% will get Cs, and the percentage of Bs and As will be the same as the percentage of Ds and Fs respectively). No teacher actually does this, though.
C grade
C
C
C
below a grade a, above a grade c
C+
(c-) -.2(c-)
its a C a high C
A grade 68% is normally a C- or D+.
70% is usually a grade of 'C'
That is a C+
C