All etching tools are either pin-tipped or bladed. While some bladed etching tools are used for engraving, some are n...

Ravi on December 12, 2018

@pfdellapo:

Et - >Pt or B

B-some-Eg
B-some-/Eg

Pt - >Eg

Conclusion: # Eg > #/Eg

In order for this conclusion to be true, we must assume that there are at least as many pin-tipped etching tools as there are Brade etching tools, which is (B). If we assume B, then since all pin-tipped etching tools are used for engraving, then there must be more etching tools that are used for engraving than are not used for engraving since some bladed etching tools are not used for engraving.

If we have 100 of both pin-tipped and bladed etching tools, then we have 100 pin-tipped etching tools used for engraving and less than 100 bladed etching tools used for engraving since there is at least one bladed etching tool that isn't used for engraving.

alymathieu on January 21, 2019

Can someone else explain this, I don't get the instructors response above. It's not clear enough.

Ravi on February 13, 2019

@alymathieu,

Happy to help. Let's take a look at the stimulus first.

We're told that etching tools come in two types: pin-tipped and
bladed. All of the pin-tipped etching tools are used for engraving.

Pin tipped - ->engraving

The bladed etching tools are sometimes used for engraving, but they
sometimes aren't used for it.

bladed etching - some - engraving

Based on this information, the stimulus concludes that there are more
used for engraving than non-engraving.

The argument is basically saying, "Come look at all of these engraving
tools! These engraving tools have to make up more than half of all of
the etching tools."

Do you see the problem with this statement? It's assuming that there
are a ton of pin-tipped etching tools. It could just as easily be the
case that pin tipped tools make up a very small percentage of all of
the etching tools.

What would fix this problem? Well, if we knew that pin tipped etching
tools made up at least half of the total number of etching tools, then
we would for sure know that over half of the etching tools are used
for engraving, which would allow us to conclude that there are more
etching tools used for engraving than non-engraving.

The question says, "The conclusion of the argument follows logically
if which one of the following is assumed?"

This is a strengthen with a sufficient premise question. We're being
tasked with filling gap in the argument to make it valid. Since we've
already identified what the gap is and know we're looking for an
answer choice that tells us that pin tipped etching tools make up at
least half of all etching tools, let's look for the answer choice that
states this for us.

(B) says, "There are as many pin-tipped etching tools as there are
bladed etching tools."

With (B), we know that there are as many pin tipped etching tools as
there are bladed etching tools (they're 50/50). Based on what we know
from the stimulus, we know that all of the pin tipped etching tools
are used for engraving, and we also know that some (at least one) of
the bladed etching tools are also used for engraving. With this
information, we know for sure that more than half of the etching tools
have to be used for engraving, which makes the conclusion of the
stimulus that there are more etching tools used for engraving than non
engraving have to follow. (B) matches our anticipation really well,
and it's the correct answer choice, as it fills the gap we needed to
fill and allows us to properly draw the conclusion in the stimulus.

Does this make sense? Let us know if you have any more questions!