# LG And/Or rules

#### meggo

• 581
##### LG And/Or rules
« on: June 08, 2008, 02:06:36 PM »
Hi, I know I'm a new poster, but I've been really appreciative of all the info in this thread for LSAT prep. I just have a question/problem.  Normally, LG are not problem but occasionally I'm becoming confused about when to use an 'and' and when to use  an 'or'. I recognize this is a pretty basic english grammar skill but anyway...

for example, in LSAT super prep, test prep B, in the second game there is a rule that deals with and/or. I don't think I'm allowed to post the rule though so anyway.....

I had originally diagrammed this as (no L) AND (no O) then it must contain F AND S. The answer has it as (no L) OR (no o) then it must....

why it is an 'or' and not an 'and'? I also have this problem with 'nor'. For example if it said, If the park contains neither L nor O, then it contains F and S. I get confused if I should diagram that as (no L) or (no O), or, (no L) and (no O).

Apologies for lack of ability in being able to diagram this properly but I hope someone understands what I'm talking about and is able to help, or can redirect me!

#### LSATHell

• 103
##### Re: LG And/Or rules
« Reply #1 on: June 08, 2008, 07:33:18 PM »
Most difficult grouping game by a long way.

Rule 1
M -> notY
Rule 2
F -> notP
Rule 3
notY -> L or O
L and O -> Y (second part of rule)
Rule 4
notL or notO -> F and S

Notice in rule 4, the 'not' negates the entire condition, including the 'and.'

#### meggo

• 581
##### Re: LG And/Or rules
« Reply #2 on: June 08, 2008, 08:21:25 PM »
ah I didn't realize a not condition would negate the 'and', that was my problem. I'm relieved that's one of the most difficult grouping games. I guess that would also explain the neither/nor thing. Neither would negate the 'nor' aspect making it an 'and'? Is this right?

#### LSATHell

• 103
##### Re: LG And/Or rules
« Reply #3 on: June 09, 2008, 06:47:04 PM »
ah I didn't realize a not condition would negate the 'and', that was my problem. I'm relieved that's one of the most difficult grouping games. I guess that would also explain the neither/nor thing. Neither would negate the 'nor' aspect making it an 'and'? Is this right?

Neither/nor just means not both.

#### Nervous Wreck

##### Re: LG And/Or rules
« Reply #4 on: June 09, 2008, 07:05:26 PM »
What's the contrapositive of this:

If A, then neither B nor C.

Is it "If either B or C, then not A"?

#### FatUncle

##### Re: LG And/Or rules
« Reply #5 on: June 09, 2008, 07:38:18 PM »
Yes.

#### meggo

• 581
##### Re: LG And/Or rules
« Reply #6 on: June 09, 2008, 08:41:22 PM »
ah, okay. Thanks. I know that's a pretty basic construct but yeah, thanks for spelling it out for me!