1958 AMC 12 Problem 44

Attempt Problem 44 of the 1958 AMC 12 below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 1958 AMC 12 solutions, or check the answer key.

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44.

Given the true statements:

1.1. If aa is greater than b,b, then cc is greater than d.d.

2.2. If cc is less than d,d, then ee is greater than f.f.

A valid conclusion is:

If aa is less than b,b, then ee is greater than ff

If ee is greater than f,f, then aa is less than bb

If ee is less than f,f, then aa is greater than bb

If aa is greater than b,b, then ee is less than ff

none of these

Answer: E
Concepts:logical deductioncounterexample
Difficulty rating: 1360
Small Hint:

Represent the comparisons as propositions and distinguish each implication from its converse

Big Hint:

The second premise’s hypothesis is incompatible with the first premise’s conclusion, but that alone does not chain the implications

Solution:

Let PP mean a>b,a>b, QQ mean c>d,c>d, SS mean c<d,c<d, and RR mean e>f.e>f. The premises are PQ,SR. P\Rightarrow Q,\qquad S\Rightarrow R. The statements QQ and SS cannot both hold. The contrapositives are ¬Q¬P\neg Q\Rightarrow\neg P and ¬R¬S.\neg R\Rightarrow\neg S. None of the four proposed implications follows. For example, knowing PP gives QQ and hence ¬S,\neg S, but says nothing about R;R; knowing ¬R\neg R gives ¬S,\neg S, not P.P.

Therefore, the correct answer is E.

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Problem 44 in Other Years

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