Logic Question (SAT II Match IC)

[rob3rt]

I'm having trouble with this question. I have no idea why the answer is D.

"Some J are K." Which of the following is logically equivalent to the preceding statement?

A. Not all J are K.
B. Some K are not J.
C. All J are K.
D. Some K are J.
E. All K are J.

Whats the difference between A,B, and D?

 

[WinkOsmosis]

That question can be interpreted different ways.. depending on how you interpret the word "some".
If "some" means some but not all (standard interpretation?), then the answer is A, because if only some of J are K, then some would have to NOT be K.

But some K would definately have to equal J or else the original statement isn't true.

 

[yellowperil]

In these word problems, they use broad definitions. "Not all" can be interpreted as some or none, and "some" is defined as at least one, but possibly all.

A is wrong because it could possibly mean that no J are K
B is wrong because it could possibly mean that all Ks are not J, which means no Js are K
D is correct because even if all Ks are J, at least one J is K

 

[rob3rt]

Thank you. that makes lots of sense.

 

[yellowperil]

I think I should revise my previous post where I said: ""Not all" can be interpreted as some or none, and "some" is defined as at least one, but possibly all."

I should've said "not all" can be interpretated as some, which does not include all, or none. But as long as I conveyed the right idea I hope it's OK