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August 20, 2014

August 20, 2014

Posted by **heatherly** on Saturday, June 6, 2009 at 2:52am.

8 If a number is divisible by 3, then the sum of the digits of that number is divisible by 3.

The sum of the digits of a number is not divisible by 3. Therefore the number is not divisible by 3.

- math -
**MathMate**, Saturday, June 6, 2009 at 3:19pmIt is a case of denying the conclusion.

Let

A=a number is divisible by 3

B= the sum of the digits of that number is divisible by 3

The hypothesis is

If A --> B

A case of affirming the hypothesis (modus ponendo ponens):

126 is divisible by three, therefore the sum of its digits is divisible by three.

A case of denying the consequence (modus tollens):

The sum of the digits of 17 is not divisible by three, therefore 17 is not divisible by 3.

See

http://en.wikipedia.org/wiki/Modus_ponens

http://en.wikipedia.org/wiki/Modus_tollens

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