Equations - Al and his father

Date: 06 Dec 94
From: Rich Allaire/NJ
Subject: help

Can you please help? My son and I differ on his homework.
It was:  Write an equation for each problem then solve it.
(I'm only sending one.)
 
Al's father is 45 years old. This is 15 more than twice Al's age. 
How old is Al?
 
Thanks - Rich
74775.260@compuserve.com

Date: Tue, 6 Dec 1994
From: Dr. Sydney
Subject: Re: help

Dear Rich:

        Thanks for writing Dr. Math!  I think if we break down the word
problem we can find an equation that will work.  Okay, let's call Al's age
x.  Then we know that twice Al's age will be 2x.  Fifteen more than twice
Al's age will be 2x + 15.  The problem says that Al's father's age (45) is
fifteen more than twice Al's age, so that means 45 = 2x + 15. So, there is
an equation for the problem.  To solve it, subtract 15 from both sides to
get 30 = 2x.  Then divide both sides by 2 to get x = 15.  So, Al must be
fifteen years old.  

Does this answer make sense?  You can check it by asking yourself is 15 more
than two times 15 equal to 45?  Indeed, it is 2 x 15 = 30, and 15+30=45.
So, we did it correctly.  Do you see how we got everything?

In general, on problems of this type, you want to give a name to what you
don't know (an x or any other letter you like, or really any symbol you
want!), and then write down what you do know in terms of your new
symbol/name.

I hope this helps.  If you have any other questions, please feel free to
write back.

--Sydney, Dr. "Math rocks"