vikram4689,
First of all, for clarity, here are all three sentences, with the other grammar mistakes corrected.
(a)
CLP-300 laserjet printer emits only 43 decibels of noise far fewer than do most other laserjet printers.
(b)
CLP-300 laserjet printer emits only 43 decibels of noise, far fewer than do most other laserjet printers.
(c)
CLP-300 laserjet printer emits 43 decibels fewer than do most other laserjet printers.
(b) is correct. Here, the phrase "43 decibels" quantifies the amount of noise the CLP-300 laserjet printer makes, and points out that this level of noise is less than that of other printers. The structure of this sentence is very clear.
(c) is also correct, and says something quite different. Here, the phrase "43 decibels" is not the level of noise of any one printer, but rather than
difference between the CLP-300 laserjet printer and (presumably) the next noisiest printer. The structure of this sentence is very clear.
(a), I would argue, is ambiguous, because it's in a grey area between what (b) conveys and what (c) conveys --- (b) & (c) give two different meanings to the "43 decibel" quantity, and it's unclear which of these two (a) intends. That, in a nutshell, the problem caused by the missing comma.
For more on how the comma changes the meaning, read:
1)
https://magoosh.com/gmat/2012/that-vs-which-on-the-gmat/
2)
https://magoosh.com/gmat/2012/gmat-gramm ... modifiers/
Here, the comma is even more tricky, because there's a comparison. In general
structure #1 = A is P, more/less than B
structure #2 = A is P more/less than B
Both compare A & B. Statement #1 gives the value/signification of A itself, P, and then adds secondarily, this happens to be more or less than B. In statement #2, P is very specifically the
difference between A and B.
For example
Structure #1 = I earn $30,000, more than Fred does.
Structure #2 = I earn $30,000 more than Fred does.
In the first, $30K would be the actual value of my salary, and then I also add, it's more than the value of Fred's salary. In the second, we have no idea of the actual value of my salary, because the figure $30K is now the
difference between my and Fred's salaries. In the first case, we know I made $30K, and Fred makes less --- maybe $29K, maybe $25K, etc. In the second, all we know is the difference --- perhaps I make $100K and Fred makes $70K, or I make $450K and Fred makes $420K. Do you see the stark difference here?
Finally, your last sentence ...
(d)
CLP-300 laserjet printer emits only 43 decibels of noise, far quieter than most other laserjet printers.
... is missing a verb after the comparison:
(d2)
CLP-300 laserjet printer emits only 43 decibels of noise, far quieter than are most other laserjet printers.
Now, in this form --- quieter (describing relative noise level) is a perfectly appropriate modifier for "43 decibel." What bothers me about this is the incomplete parallelism --- "The CLP-300 . . .
emits . . [and] other laserjet printers
are ..." Because of that parallelism problem, I don't believe this sentence would be correct on GMAT SC.
Does all this make sense?
Mike
