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### Modus Ponens

```
Date: 07/10/2001 at 16:15:50
From: Erin Cushing
Subject: Math logic

This is my question:

A man is x years old at the year x squared, and he was born in 1806.
I am supposed to solve for x.

I got the answer, 43, but I don't know how to explain it in terms of
logic. When I asked my teacher, he said to use the Modus Ponens rule
and I shouldn't have a problem, but I am.

```

```
Date: 07/10/2001 at 17:55:38
From: Doctor Jaffee
Subject: Re: Math logic

Hi Erin,

The Modus Ponens rule says that if you know that a statement, P, is
true and that if P is true, then the statement Q is true, you can
conclude that Q is true.

Your conclusion was that the man was 43 years old in 1849, so that
must be the statement Q.

Now, what is the mathematical relation between the year a person was
born, the current year, and the the person's age?  If you can express
that statement as an equation in terms of x, you will have the
statement P.

Give it a try and if you want to check your solution with me, write
back. If you are having difficulties, let me know and show me what you
have done so far, and I'll try to help you some more.

Good luck.

- Doctor Jaffee, The Math Forum
http://mathforum.org/dr.math/
```
Associated Topics:
High School Logic

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