Question: if-then conditional statements

Aiesha G. · April 2015

Using a kaplan book in conjunction with these videos and can use some help! Can anyone explain Kaplan's answer for the part B? I could have sworn it was an error.

If Megan buys a juicer, then she buys kale or mangos.

A. What do we know if megan buys a juicer?
My answer: she bought mangos, kale, or both.
B. What do we know if megan buys neither mangos nor kale?
My answer: nothing. I thought that no logical deductions could be made from this statement because this is the necessary condition not the sufficient condition.
Kaplans answer: then she can't have bought a juicer

ddakjiking · April 2015

Answer B is the contrapositive of the statement:
If Megan buys a juicer, then she buys kale or mangos.

When you take the contrapositive, you negate and switch "or" to "and". So if Megan does not buy kale "AND" mango, then Megan did not buy the juicer.

Aiesha G. · April 2015

Ok that makes sense! Thanks a lot

ddakjiking · April 2015

No problem. Another way to simplify that argument is
J-> K or M

contra: notK and notM -> notJ

alexroark5 · April 2015

@"Aiesha G." I would review JY's lessons on logic. This is what is called demorgan's law. You can deduce she did not buy a juicer.

http://7sage.com/lesson/contrapositives-demorgans-law/

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