Ratna wrote:I am totally confused as to when to use less and when to use fewer, similarly when to use greater than and when to use more than...

No matter how many time i read and understand, when the question comes in the test i always end up marking the wrong answer.

Can someone help me with good examples so that i can remember?

Appreciate your help!!!!!

Are you referring to sentence correction? If so, use "fewer" when you have a number of distinct and separable items and use "less than" when you're dealing in parts of a whole or with an indistinct substance. For example, pile A has fewer marbles than pile B (because each marble is its own distinct unit). Bucket A, however, has less water than bucket B (because the water is a fluid that can't be broken down into units. But it could be phrased as: Bucket A has fewer cubic centimeters of water than Bucket B" because a cubic centimeter is an individual unit.

Great explanation, InkyBinky - and just since the topic is up, let me add:

-the distinction really comes down to "Singular" (one entity, like "water" or "sand") vs. "Plural" (multiple items, like "gallons of water" or "grains of sand")

-it's important, then, to note these particular idioms because they'll correspond nicely with other GMAT errors (singular/plural pronouns; singular/plural verbs; comparisons in which you'd have more/fewer of one than another)

So, those idioms would fall into a few camps:

Singular vs. Plural
Much vs. Many
Less vs. Fewer
Amount vs. Number
Little vs. Few

Note: I'm working on making this table look prettier, but hopefully this is alright for now.

Examples:

There is so much pollution in the air that the city has warned people to stay inside. ("Pollution" is singular)
There are so many toxins in the water that the beach will be closed for the rest of the summer. ("Toxins" is plural)

There is less water in the Atlantic Ocean than in the Pacific. ("water" is singular)
There are fewer whales in the Atlantic Ocean than in the Pacific. ("whales" is plural)