2,632 views
1 votes
1 votes
Show that these statements are inconsistent: “If Miranda does not take a course in discrete mathematics, then she will not graduate.” “If Miranda does not graduate, then she is not qualified for the job.” “If Miranda reads this book, then she is qualified for the job.” “Miranda does not take a course in discrete mathematics but she reads this book.”

how to approach?

3 Answers

Best answer
1 votes
1 votes
AND all the given requirements and all should be true simultaneously.(Using shortcut for statements)

1. ~DM -> ~Graduate

2. ~Graduate -> ~Job

3.  books -> Job qualified

4. ~DM AND Books

Assume all of them to be true. Then from 4th point both should be true. As ~DM is true ~graduate should be true(point 1). As ~graduate is true, ~job should be true(point 2).

Now in 3rd point books is true (from 4) and for point 3 to be true, job qualified should be true but is is already false from point 2.

Hence all of these 4 conditions cannot be true simultaneously.
selected by
2 votes
2 votes

A set of statements are called Logical Inconsistent when they can't be true at the same time.

For example, If we have some statements as $p,q,r,s$ then if we make a set of some logical statements from these statements $p,q,r,s$ like $\{p \rightarrow \;\sim q , r\rightarrow q, \;\sim p \rightarrow r\}$ then this set of logical statements i.e. $\{p \rightarrow \;\sim q , r\rightarrow q, \;\sim p \rightarrow r\}$ is called logically inconsistent if it can't be true at the same time and logically consistent if we can get at least one possible set of boolean values of $p,q,r,s$ for which all the statements from the set  $\{p \rightarrow \;\sim q , r\rightarrow q, \;\sim p \rightarrow r\}$ are true simultaneously. We can check it by making truth table also. In truth table if we get atleast one tuple for which  all the statements of the set $\{p \rightarrow \;\sim q , r\rightarrow q, \;\sim p \rightarrow r\}$ are true then this set is called logically consistent  otherwise logically inconsistent.

Now, In this question,

Let,

$p$ = Miranda does not take a course in Discrete Mathematics

$q$ = She will not graduate 

$r$ = She is not qualified for the job

$s$ = She reads this book

Now, according to given statements in the question,

We have to check logical consistency for the set :-

$\{p\rightarrow q,\; q\rightarrow r,\;s\rightarrow \sim r, \; p\wedge s\}$

Now, I am trying to make it consistent and checking that I will get success or not for this goal.

For logical consistency, all statements must be true simultaneously.

So, statement $p\wedge s$  must be true. It means both $p$ and $s$ must be true.

Now, statement $s\rightarrow \sim r$ should also be true , So, $r$ must be false.

and if $r$ is false then statement $q\rightarrow r$ must be false.

So, all statements can't be true at the same time.So, It means I have failed in my goal.

So, We can conclude that given set of logical statements is logically inconsistent. 

Related questions

0 votes
0 votes
1 answer
2
pavan singh asked May 7, 2023
705 views
Given: (p$ \vee$ q) is True. Find the truth value of statements, 1. p is false or q is true. (Can't determine) 2. If p is false then q is true. (True) is my answer correc...
3 votes
3 votes
1 answer
3
Reshu $ingh asked May 30, 2019
1,927 views
Are these propositions?1.This sentence is true2.This sentence is falseAren’t these liar paradox?
0 votes
0 votes
2 answers
4