Africa's black rhino population in the mid-1970's numbered about 20,00

"more than" redundant.
their- pronoun doesn't agree in number.

A best.

we can count rhinos so 'amount' does not seem appropriate, hence c and e are out.
d is wordy, and using 'that' in B is wrong. Hence A.

But, i wonder if there is any thing like 'ten times less' ....

is it because the population of 1997 is already mentioned here, that the use THAT is redundant?

had it been something like this

Africa's black rhino population in the mid-1970's numbered about 20,000, ten times THAT of 1997.

would it be correct?

Perfect

Try to fit this concept here.

One of the primary distinctions between our intelligence and that of other primates may lay not so much in any specific skill but in our ability to extend knowledge gained in one context to new and different ones.

Graduate Management Admission Council (GMAC) (2012-04-13). The Official Guide for GMAT Review (Kindle Locations 36593-36595). John Wiley and Sons. Kindle Edition.

THE Main problem with D is that
"ten time more than" mean 11 times the population. This is not logic.

"ten time as many as" mean 10 times

is my thinking correct?

So you would think!! But surprisingly, I have seen Official questions, where such "mathematical anomalies" are considered acceptable in the correct answer.

D is primarily more verbose than the correct answer A.

(a) the estimated population--- a quantity compared with another quantity: correct comparison and correct choice.
(b) that of their estimated population ---- The problem is the plural pronoun ‘their’; there is no justification for using a plural
(c) more than the population's estimated amount ---- ‘ten times as x means 10x; ten times ‘more than x’ means 11 x
(d) more black rhinos than their population estimate--- same as C ; in addition the problematic ‘their’
(e) more than that of their population's estimated amount --- same as that of D.

Africa's black rhino population in the mid-1970's numbered about 20,000, ten times the estimated population of 2,000 in 1997.

(a) the estimated population
This version is not perfect, in that "20,000, ten times the estimated population of 2000" is a little awkward and does not make complete sense, but basically it logically compares 20,000 with 2000.

(b) that of their estimated population
This choice has two issues. First there is no logical antecedent for "that". Ten times what of the estimated population? Second, though there are multiple black rhinos in the population of black rhinos, in the sentence itself, there is no logical antecedent for "their".

(c) more than the population's estimated amount
"ten times more" is not logical. The point is that 20,000 is ten times 2,000. "ten times more", if it means anything, means eleven times, and eleven times 2000 is 22,000, not 20,000. "amount" does not correctly refer to a countable number. Also, "the population's estimated amount of 2,000" is awkward and does not clearly convey that the number of rhinos in the population was 2,000.

(d) more black rhinos than their population estimate
This version repeats the "ten times more than" error seen in C, and "their" has no logical antecedent. Also, this version illogically compares "black rhinos" to "their population estimate of 2000".

(e) more than that of their population's estimated amount
This version repeats the "ten times more than" flaw and the "amount" error seen in C. "that" is unnecessary and has no logical antecedent. "their" has no logical antecedent. The entire choice is unnecessarily wordy and does not directly compare 20,000 with 2,000, but rather compares 20,000 with "that of ... 2,000", a comparison that conveys nothing that makes sense.

The best answer is A.

Hi egmat

Bit confused while applying comparison here.
Initial no: In 1997, 2000
Mid 1970: 20,000 (10 times of 2000)

More than phrase in C,D and E suggests value more than 20,000 in mid 1970s which is incorrect.

For (B) does that jump over noun ten times and
noun phrase in the mid-1970's numbered about 20,000, to suggest illogical
comparison between rhino population and esteemed population.

WR,
Arpit.

daagh GMATNinja
Can we eliminate options B and D on the basis of the pronoun that ?
"that" takes a singular noun(population). So the sentence looks like
"Africa's black rhino population in the mid-1970's numbered about 20,000, ten times population of their estimated population of 2,000 in 1997."
Is this a correct approach?

Yup, that's exactly how I would think of it. The only singular noun "that" could possibly refer back to is the population. So for (B), we get "...ten times the population of their estimated population", exactly as you said. For (E), we get "...ten times more than the population of their population's estimated amount." Both are pretty ridiculous. (And "their" is a problem in both of those too, for whatever it's worth.)

The GMAT seems to love using "that" as a pronoun for some reason, so I promise that you'll see this again.

GMATNinja Could you please help with my query for pronoun ambiguity. As of now, in reference to GMAT, I feel that Possessive pronoun can refer possessive noun. So, if my understanding is correct, then please tell me whether "their"in this SC problem can refer "Black Rhinos' ".

In (B) and (E), there's absolute no chance that "their" could refer to "black rhinos". Why? The phrase "black rhinos" doesn't actually appear in either of those answer choices. We have "Africa's black rhino population" in the non-underlined portion, and that's unambiguously singular. The sentence says "Africa's black rhino population", not "the black rhinos' population". So "their" is wrong in both (B) and (E).

In (D), "their" actually HAS to refer to "black rhinos", since it's the only plural noun that appears earlier in the sentence. But that still doesn't make sense: "Africa's black rhino population in the mid-1970's numbered about 20,000, ten times more black rhinos than [the black rhinos'] population estimate." It's pretty messy and illogical to compare the number of black rhinos to "the black rhinos' population estimate." It's also weird to suggest that the rhinos somehow "possess" a population estimate.

I hope this helps!

Hi Arpit,
Here in B that is used as a pronoun. When that is used as a pronoun it creates a new copy of what it is used for.
For eg: Like the poetry of Bruce Willis, that of Chuck Norris is flowery and pretty
above sentence can also be written as:
Like the poetry of Bruce Willis, the poetry of Chuck Norris is flowery and pretty.

Now getting back to this question. Here we do not need a copy as the estimated population is already part of the answer choice B. So that is not pointing to anything. Hence incorrect.

I hope it helps.

Please give kudos if you like the explanation.

(A) the estimated population

1) a correct comparison.

(B) that of their estimated population

1) "that" stands for a singular and preciding noun: "Africa's black rhino population" is the only such noun. If you replace "that" with that biiig noun, you get:

Africa's black rhino population in the mid-1970's numbered about 20,000, ten times Africa's black rhino population of their estimated population of 2,000 in 1997. an illogical comparison.

2) "their" refers to a plural noun, but there is no such one.

(C) more than the population's estimated amount

1) "population" means the number of organisms: Here is possibly the best definition:

A population is the number of organisms of the same species that live in a particular geographic area at the same time, with the capability of interbreeding.
Hence, "population's number", "population's amount", "number of population", and "amount of population" are all redundant.

2) amount refers to an uncoutable noun, but "rhino" is countable.

(D) more black rhinos than their population estimate

1) "their" refers to a plural noun: "black rhinos" is the only such noun. This choice illogically compares "black rhinos" with their "population estimate".

(E) more than that of their population's estimated amount

1) "that" stands for a singular and preciding noun: "Africa's black rhino population" is the only such noun. If you replace "that" with that biiig noun, you get:

Africa's black rhino population in the mid-1970's numbered about 20,000, ten times Africa's black rhino population of their estimated population of 2,000 in 1997. an illogical comparison.

2) "their" refers to a plural noun, but there is no such one.

3) "population" and "amount" are redundant

4) amount refers to an uncoutable noun, but "rhino" is countable.

Africa's black rhino population in the mid-1970's numbered about 20,000, ten times the estimated population of 2,000 in 1997.

(A) the estimated population Correct answer - no apparent errors.

(B) that of their estimated population "that of their" illogically refers to a possession of "their" ie; something possessed by the black rhino population. Eliminate.

(C) more than the population's estimated amount Incorrect usage of "amount" for a countable. Eliminate.

(D) more black rhinos than their population estimate "Population" is being incorrectly compared to "estimate". Eliminate.

(E) more than that of their population's estimated amount Same error as in (C). Eliminate.

Hope this helps.

I am not sure whether this makes 100% sense but '20,000 is ten times 2,000' and 'not ten times more than 2,000' because the latter would make the number more than 20,000. So, C, D, and E are out. Between A and B, A it is. In B, 'that' refers to population and it doesn't make any sense.