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#1 2013-09-17 23:15:01

Registered: 2013-09-17
Posts: 1

nn x nnn = nnnn

Years ago, somehow, I stumbled across a problem.  Using only the digits 1-9 (not zero, and no duplications) how many combinations of nn x nnn = nnnn.  You can see that it is a 2 digit number multiplied by a three digit number = a four digit number, using only the 9 digits.  I have no idea what this problem was called (I presume it has a name...?) and I can`t find a reference to it.  Have you heard of this one?  I ended up writing a computer program to generate all the combinations and tell me the answer.  Yes it`s a cheat, but there are a lot of possible combinations...:)  Not many valid answers, though.  Peter


#2 2013-09-17 23:24:34

From: Bumpkinland
Registered: 2009-04-12
Posts: 92,928

Re: nn x nnn = nnnn


Welcome to the forum. They are called alphametics or cryptarithms  and can be generally solved by computer. They can also be solved by hand but would take too long for ones with multiple solutions.

There are 7 solutions to

ab x cde = fghi

In mathematics, you don't understand things. You just get used to them.

I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.


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