assignment 14

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course MTH 151

014. Truth Tables

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Question: `q001. There are 8 questions in this set.

If each of the propositions p and q can be either true or false, what combinations of truth values are possible for the two propositions (e.g., one possibility is that p is false and q is true; list the other possibilities)?

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Your solution:

TF

FT

TT

FF

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Given Solution:

It is possible that p is true and q is true.

Another possibility is that p is true and q is false.

A third possibility is that p is false and q is true.

A fourth possibility is that p is false and q is false.

These possibilities can be listed as TT, TF, FT and FF, where it is understood that the first truth value is for p and the second for q.

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Question: `q002. For each of the for possibilities TT, TF, FT and FF, what is the truth value of the compound statement p ^ q ?

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Your solution:

TT- TRUE

TF-FALSE

FT- FALSE

FF-FALSE

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Given Solution:

p ^ q means 'p and q', which is only true if both p and q are true.

In the case TT, p is true and q is true so p ^ q is true.

In the case TF, p is true and q is false so p ^ q is false.

In the case FT, p is false and q is true so p ^ q is false.

In the case FF, p is false and q is false so p ^ q is false.

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Question: `q003. Write the results of the preceding problem in the form of a truth table.

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Your solution:

TTT

TFF

FTF

FFF

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Given Solution:

The truth table must have headings for p, q and p ^ q. It must include a line for each of the possible combinations of truth values for p and q. The table is as follows:

p q p ^ q

T T T

T F F

F T F

F F F.

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Question: `q004. For each of the possible combinations TT, TF, FT, FF, what is the truth value of the proposition p ^ ~q?

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Your solution:

TT-FALSE

TF-TRUE

FT-FALSE

FF-FALSE

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Given Solution:

For TT we have p true, q true so ~q is false and p ^ ~q is false.

For TF we have p true, q false so ~q is true and p ^ ~q is true.

For FT we have p false, q true so ~q is false and p ^ ~q is false.

For FF we have p false, q false so ~q is true and p ^ ~q is false.

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Question: `q005. Give the results of the preceding question in the form of a truth table.

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Your solution:

TTFF

TFTT

FTFF

FFTF

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Given Solution:

The truth table will have to have headings for p, q, ~q and p ^ ~q. We therefore have the following:

p q ~q p^~q

T T F F

T F T T

F T F F

F F T F

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Question: `q006. Give the truth table for the proposition p U q, where U stands for disjunction.

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Your solution:

TTT

TFT

FTT

FFF

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Given Solution:

p U q means 'p or q' and is true whenever at least one of the statements p, q is true. Therefore p U q is true in the cases TT, TF, FT, all of which have at least one 'true', and false in the case FF. The truth table therefore reads

p q p U q

T T T

T F T

F T T

F F F

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Question: `q007. Reason out the truth values of the proposition ~(pU~q).

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Your solution:

TT- FALSE

TF-FALSE

FT-TRUE

FF-FALSE

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Given Solution:

In the case TT p is true and q is true, so ~q is false. Thus p U ~q is true, since p is true. So ~(p U ~q) is false.

In the case TF p is true and q is false, so ~q is true. Thus p U ~q is true, since p is true (as is q). So ~(p U ~q) is false.

In the case FT p is false and q is true, so ~q is false. Thus p U ~q is false, since neither p nor ~q is true. So ~(p U ~q) is true.

In the case FF p is false and q is false, so ~q is true. Thus p U ~q is true, since ~q is true. So ~(p U ~q) is false.

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Question: `q008. Construct a truth table for the proposition of the preceding question.

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Your solution: TTFTF

TFTTF

FTFFT

FFTTF

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Given Solution:

We need headings for p, q, ~q, p U ~q and ~(p U ~q). Our truth table therefore read as follows:

p q ~q pU~q ~(pU~q)

T T F T F

T F T T F

F T F F T

F F T T F

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Question: `q008. Construct a truth table for the proposition of the preceding question.

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Your solution: TTFTF

TFTTF

FTFFT

FFTTF

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Given Solution:

We need headings for p, q, ~q, p U ~q and ~(p U ~q). Our truth table therefore read as follows:

p q ~q pU~q ~(pU~q)

T T F T F

T F T T F

F T F F T

F F T T F

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Assignment 14

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course mth 151

Question: `q3.3.5 rewrite using if then ' all marines love boot camp '.

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Your solution:

If he is a marine, he loves boot camp

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Given Solution:

`a** The statement is equivalent to 'If it's a Marine, it loves boot camp' or equivalent.

The statement is not equivalent to 'if it is boot camp, then all Marines love it', which is the converse of the original statement. **

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Question: `q3.3.18 ~p false q false p -> q true

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Your solution:

true

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Given Solution:

`a** Since ~p is false then p is true.

Since q is false it follows that p -> q is of the form T -> F, which is false.

The conditional is false when, and only when, the antecedent is true and the consequent false. **

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Question: `qQuery 3.3.36 write in symbols 'If we don't bike, then it does not rain.'

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Your solution:

p-r

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Given Solution:

`a** If p stands for 'don't bike' and r for 'it rains' then the statement would be p -> ~r. **

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Question: `qQuery 3.3.48 q true, p and r false, evaluate (-r U p) -> p

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Your solution:

false

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Given Solution:

`a** The antecedent (~r U p ) would be true, since ~r true and p false.

The consequent p would be false.

Since the antecedent is true and the consequent false, the conditional is false. **

MORE DETAILED SOLUTION

r is said to be false, so ~r is true

p is said to be false

Therefore the disjunction (~r U p) would be a disjunction of a true and a false statement.

A disjunction is true if at least one of the statements is true, so (~r U p) is true.

The conditional (~r U p) -> p therefore consists of an antecedent which is true, and a consequent which is false.

By the rules for a conditional, the statement is therefore false.

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Question: `qQuery 3.3.60 truth table for (p ^ q) -> (p U q)

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Your solution:

Tttt

Tfftt

Ftftt

fffft

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Given Solution:

`a** The headings would be p, q ,(p^q), (pUq), (p^q)->(pUq)

Row 1 would read T T T T T

Row 2 would read T F F T T

Row 3 would read F T F T T

Row 4 would read F F F F T

The common sense of this is that whenever both p and q are true, then the statement 'p or q' must be true. That's what means to say (p ^ q) -> (p U q).

The fact that this statement is true is indicated by the last column of the truth table, which has True in every possible case. **

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Question: `qQuery 3.3.74 (formerly 3.3.72). This wasn't assigned but it is similar to assigned questions and should be answered: What is the negation of the statement 'if loving you is wrong then I don't want to be right' ?

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Your solution:

LOVING YOU IS WRONG AND I WANT TO BE RIGHT

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Given Solution:

`a** The negation has to have the exact opposite truth values of the original statement.

It is difficult and confusing to try to negate a conditional. It is much easier to translate the conditional to a disjunction then negate the disjunction. It is easy to negate the disjunction using deMorgan's Laws.

Since p -> q is identical to ~p U q, the negation of p -> q is ~ ( ~p U q), which by de Morgan's Law is ~ ~p ^ ~q, or just p ^ ~q.

So the negation would ge 'loving you is wrong AND I want to be right.

COMMON ERROR AND NOTE: If loving you is wrong, then I want to be right.

INSTRUCTOR COMMENT:

The negation of a conditional can't be a conditional (a conditional is false in only one case so its negation would have to be false in three cases). **

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