Hi Pdgmat2010. I have tried to answer each of your questions:

1) "that which" is not inherently incorrect. It can be correct or incorrect depending on whether the reference is correct. In this construct, 'which' begins a noun (adjectival) modifier that targets to the antecedent of 'that'. For instance, "My shoe is better than that which we found in the box". this is a correct sentence. 'that' refers to 'shoe'. 'which we found in the box' is a modifier for 'that' (it identifies/describes which shoe is discussed)

In this construct, "that" is the pronoun, not the conjunction "that". "John told his employer that which...." will probably be an incorrect sentence because 'that' in this case is a conjunction that should introduce a subordinate clause. 'that' in this case is not a pronoun that is referring to a noun elsewhere in the sentence. That's why it makes no sense to follow it with a noun modifier (which...). Of course what completes the sentence can make a difference.

2) The first error in C is the incorrect use of the idiom: "as much as". To express equality in a comparison, the two as are needed. "as much compared to" is incorrect. "as much as" would have been better.

3) 'that' as used here is a singular pronoun. It stands for "the amount". "The amount emitted by these cars is twice that emitted by those cars" This is not a new rule that you don't know. It's just a singular pronoun referring to a specific noun and in doing so maintaining a parallel structure. So there isn't anything wrong. Another example might be: "The food sold at restaurant A is as pricey as that sold at B".

A full discussion of this question can be found at GMATPrep Question 2167. To test yourself with similar questions, create a drill and set topic='Parallelism, Comparison & Pronouns' and difficulty='600-700'

hope that helps,
-Patrick

Thanks a lot Patrick.
A few takeaways for me from your reply

1. 'that' is used as a pronoun in some cases where it replaces the antecedent that came in the first part of the sentence.

The race course in Pune is much better than that in Bombay. [that - race course]

2. 'that which' is a correct usage when 'that' refers to a noun in the beginning of the sentence and 'which ... ' acts as a modifier for 'that'.

3.To express equality in a comparison, the two as are needed.



4. twice that
The cost of coffee at Costa is twice that at Starbucks. ( is this usage of twice that correct?)

Patrick_GMATFix wrote:Hi Pdgmat2010. I have tried to answer each of your questions:

1) "that which" is not inherently incorrect. It can be correct or incorrect depending on whether the reference is correct. In this construct, 'which' begins a noun (adjectival) modifier that targets to the antecedent of 'that'. For instance, "My shoe is better than that which we found in the box". this is a correct sentence. 'that' refers to 'shoe'. 'which we found in the box' is a modifier for 'that' (it identifies/describes which shoe is discussed)

In this construct, "that" is the pronoun, not the conjunction "that". "John told his employer that which...." will probably be an incorrect sentence because 'that' in this case is a conjunction that should introduce a subordinate clause. 'that' in this case is not a pronoun that is referring to a noun elsewhere in the sentence. That's why it makes no sense to follow it with a noun modifier (which...). Of course what completes the sentence can make a difference.

2) The first error in C is the incorrect use of the idiom: "as much as". To express equality in a comparison, the two as are needed. "as much compared to" is incorrect. "as much as" would have been better.

3) 'that' as used here is a singular pronoun. It stands for "the amount". "The amount emitted by these cars is twice that emitted by those cars" This is not a new rule that you don't know. It's just a singular pronoun referring to a specific noun and in doing so maintaining a parallel structure. So there isn't anything wrong. Another example might be: "The food sold at restaurant A is as pricey as that sold at B".

A full discussion of this question can be found at GMATPrep Question 2167. To test yourself with similar questions, create a drill and set topic='Parallelism, Comparison & Pronouns' and difficulty='600-700'

hope that helps,
-Patrick

yes Pdgmat2010; the sentence you typed is correct because replacing 'that' with its antecedent does not introduce any error: "The cost of coffee at A is twice the cost of coffee at B."

-Patrick