Math logic problem.

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<p>Hi all.</p>

<p>This is my first post, so hi to everyone.</p>

<p>I am working on my math skills. I found a question that I just can't understand the solution. I hope you can help me.</p>

<p>A certain communication system is made up of 40 symbols. A maximum of two symbols placed to- gether, order not mattering, make up a word. What is the maximum number of words in this communica- tion system?</p>

<p>Maximum is 2 symbols and I can choose the same symbol, so 40x40 and I need to add another 40 because 1 symbol is also makes up a word. 40x40+40= 1640. Which is incorrect.</p>

<p>The solution in the book states:</p>

<p>Answer: 840
There are 40 </p>

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<p>see, the question indicates “order not mattering”
what does that mean?
let’s say you have two symbols A and B for example
AB and BA is the same thing, because the order does not matter
so when you consider the maximum possible combinations using 40 times 40, you actually consider AB and BA as different expressions
so you have to delete half of your results</p>

<p>hope my answer will be helpful :D</p>

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<p>Thank you!!! </p>

<p>Now I got it.
I just needed a good explanation.</p>

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<p>you are welcome :)</p>

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<p>true, sheldonwang</p>