Officials at the United States Mint believe that

[jlucero]

Officials at the Unites States Mint believe that the Sacagawea dollar coin will be used more as a substitue for four quaters rather than for the dollar bill because its weight, only 8.1gms, is far less than four quaters, which weigh 5.67 gms each.

a) same
b) more as a substitute for four quaters than the dollar bill because it weighs only 8.1gms, far lighter than
c) as a substitue for four quarters more than for the dollar bill because it weighs only 8.1 gms, far less than

"far lighter than", "far less than" are appositive which should modify the a noun/number immediately preceding. So, "far lighter than" must modifies 8,1 gms, making it nonsense. B is incorrect.

is my thinking correct?

Check your definition of appositive, because these phrases aren't renaming the noun, but describing them and their properties.

[xiaonvhai123]

Hi, experts:
I have a question about " far lighter than" and " far less than".
What's the difference between this two? Are both of them correct?

When I did this problem, I though we can never use "less" do describe "grams" (IMO grams should be a countable thing...), so I kill ACE at the first glance...

Would you like to help me on this point?

An idiom to memorize:

A THING is lighter than another THING. (compares nouns)
Something has a WEIGHT that is less than another WEIGHT (compares two thing's properties)

Our sentence after the word because:

its weight, only 8.1gms, is far less than four quaters, which weigh 5.67 gms each.

B&D eliminated

Hi, experts, after a final check, I find more problems on this point.

for B:because it weighs only 8.1gms, far lighter than
it=coin, so coin can be lighter than quaters. So the comparison in B is correct.

For C: it weighs only 8.1 gms, far less than
it=coin, coin cannot far less than quaters. so...C IS WRONG!!!
Only weight can be less than another weight.

Can anyone help on this point...??

[RonPurewal]

For C: it weighs only 8.1 gms, far less than
it=coin, coin cannot far less than quaters. so...C IS WRONG!!!

first --
OFFICIALLY CORRECT ANSWERS ARE CORRECT!
do not question officially correct answers!
far too many students on this forum make the mistake of questioning the correct answers; please note that doing so is a complete waste of your time and effort. i.e., exactly 0% of the time that you spend posting "isn't this official answer wrong?" is productive, and exactly 100% of that time is wasted.

"is this correct?" is NEVER a productive question to ask about one of GMAC's correct answers -- the answer is always yes.
"is this wrong?" / "is this X type of error?" is NEVER a productive question to ask about one of GMAC's correct answers -- the answer is always no.

instead, the questions you should be asking about correct official answers, if you don't understand them, are:
"why is this correct?"
"how does this work?"
"what understanding am i lacking that i need to understand this choice?"

this is a small, but hugely significant, change to your way of thinking -- you will suddenly find it much easier to understand the format, style, and conventions of the official problems if you dispose of the idea that they might be wrong.

--

here's a simpler illustration of what is going on here:

suzy weighs far less than tom does.
suzy weighs far less than does tom.
suzy weighs far less than tom.
all of these sentences are correct -- including the last, since there's no ambiguity.

suzy weighs only 120 pounds, far less than tom.
--> this is the same essential construction as the third example above.

[RonPurewal]

IMO grams should be a countable thing...

nope. units of continuous measure don't take the "countable" descriptions, because they're not countable -- they are units in which continuous (i.e., non-countable) things are measured.
"countable" things, on the other hand, are entities that are quite literally separate (or separable), and that can only exist in whole numbers.

e.g.,
hats, shirts, and people are "countable" things.
these are actually separate entities -- you can separate them and count one, two, three, ... -- and you can't have non-whole-number quantities of them. i.e., you can't have 6.2 hats, or 2.5 shirts, or 3.45 people.

when you make comparisons with grams/dollars/gallons/liters/etc., though, you are not talking about things that are "countable" in this sense.
for instance, if i have "twenty dollars", that is in all likelihood NOT twenty individual objects -- it's a continuous unit of measure.
so, i wouldn't write "this costs fewer than 20 dollars"; instead, i write "this costs less than 20 dollars".

make sure you understand why each of the following is correct:
i have less than 50 dollars in my wallet.
i have fewer than 50 one-dollar bills in my wallet.