SOLUTION: NOT EVEN MY MATH TUTOR COULD HELP ME PLZ ANYONE! he just gave me the answer and logged off said it was fallacy by deductive reasoning?!? If the argument below is valid, name wh

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Question 472950: NOT EVEN MY MATH TUTOR COULD HELP ME PLZ ANYONE! he just gave me the answer and logged off said it was fallacy by deductive reasoning?!?
If the argument below is valid, name which of the four valid forms of argument is represented. If it is not valid, name the fallacy that is represented.

If Sally is on vacation, then Tom is at work.
If Tom is at work, then the line at the post office is long.
Therefore, if Sally is on vacation, then the line at the post office is long.

Answer by Theo(13342) (Show Source):
You can put this solution on YOUR website!
If Sally is on vacation, then Tom is at work.
If Tom is at work, then the line at the post office is long.
Therefore, if Sally is on vacation, then the line at the post office is long.
I believe this is true by the following law:
Law of syllogism: (Law of hypothetical syllogism) (reasoning by transitivity)
This law states:
p -> q (premise 1)
q -> r (premise 2)
therefore:
p -> r (conclusion)
a reference that includes that law as one of the valid arguments is shown below:
http://ux.brookdalecc.edu/fac/tlt/math/136/logic.pdf
search for:
law of syllogism (Law of hypothetical syllogism) (reasoning by transitivity)
here's another reference.
http://alameda.peralta.edu/Projects/20430/Logic...%20Philosophy%20010/Deductive%20argument%20forms.htm
search for:
hypothetical syllogism.