Q17 - If a motor is sound-insulated

[GeneW]

It would be appreciated if someone can explain why B is correct and E incorrect. Thank you.

[jan]

If you diagram the argument into conditionals, it would be

SI (sound insulated) - HA - IS

the part where it says that none of the motors manufactured by EM industries are quiet enough to use in home appliances would make it possible for us to assume that none of them are sound insulated by using contrapositive of SI - HA.
That leads to why B is correct.

E would lead us to making a mistaken negation argument. Basically, it is saying that because ~HA, it is ~ IS. We can't assume that's true.

[christine.defenbaugh]

Thanks for posting, GeneW!

withjc_4ev has basically rocked it, but I thought I'd swing in and run through this top to bottom for completeness's sake.

Since this is an inference question, the correct answer will be unpredictable, but fully supportable from the information in the stimulus.

So, let's sort out all the information in stimulus! Everything in the stimulus is about motors.

1) sound-insulated --> quiet enough for home apps
2) quiet enough for home apps --> institutional settings
3) All the EM manufactured motors are [NOT quiet enough for home apps]

Now, I could have written that third piece of information a few ways. I might have written as a conditional (If EM --> NOT quiet), or kept the 'none' language. I find it easiest, though, to consider that this is telling me that certain motors have a certain characteristic: [not quiet enough for home apps].

Interestingly, [NOT quiet enough for home apps] does not appear to be in our information....at least, not until we contrapose something. If we contrapose #1 though, we get:

If NOT quiet enough for home apps --> NOT sound insulated

This fully supports answer choice (B)! If the EM motors are NOT quiet enough for home apps, then they must NOT be sound insulated!

Let's take a brief spin through all the incorrect answers:

(A) This is an attempt to connect #1 and #2, but it's an illegal reversal of the combination. A proper combination would read: If sound insulated --> institutional settings

(C) Maybe this is true, but we have no idea! All we know is they aren't quiet. That certainly doesn't guarantee that some of them can be used in institutional settings!

(D) This is an illegal reversal of statement #1!

(E) If we know that the motors AREN'T quiet, we can't connect that to anything about institutional settings. The only way to make this connection would be to assume that if not quiet --> not institutional settings - and that would be an illegal negation of statement #2!

Only answer (B) is fully supportable by the information we are given in the premise.

Please let me know if this completely answers your question, and withjc_4ev, keep rocking out!

[DevniY511]

Hi,

I still don’t understand why E is wrong.

Here’s my working:

S: motor sound insulated
Q: quiet enough to use in home appliances
I: can be used in institutional settings
EM: manufactured by EM Industries

1. S -> Q; contrapositive: ~Q -> ~S
2. Q -> I; contrapositive: ~I -> ~Q
3. EM -> ~ Q; contrapositive: Q -> ~EM

We can get several deductions from these, including B and E:

• Answer choice (B)
1. S -> Q
3. Q -> ~EM
Which would give us S -> ~EM
It’s contrapositive: EM -> ~S is Answer choice (B)


• Answer choice (E)
2. Q -> I
3. Q -> ~EM
Which would give us I -> ~EM
It’s contrapositive: EM -> ~I is basically Answer choice (E)

What am I not getting here?