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Math Challenge IC Handout 6

 
 
PengChristina的头像
Math Challenge IC Handout 6
PengChristina - 2018年04月14日 Saturday 01:33
 

There are a few confusing points in the homework. For 6.18, I don't think we would be able to mathematically calculate that, we would have to look into a dictionary and manually count it. In 6.22, what are Martian words?


Thank you!

 
ReynosoDavid的头像
Re: Math Challenge IC Handout 6
ReynosoDavid - 2018年04月16日 Monday 10:33
 

Think of a "word" as a sequence of letters (even if it is not possible to read in English). The words in 6.18 will only have $A$' and $B$'s, for example $AABBBABAB$.

The first part of problem 6.22 was missing on the online homework. The problem should say "Suppose the Martian alphabet has 10 letters, and a Martian word is any sequence of 4 letters, allowing repeats.". It has now been corrected on the homework.

 
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PengChristina的头像
Re: Math Challenge IC Handout 6
PengChristina - 2018年04月16日 Monday 19:22
 

Thanks! I tried the Martian question but I don't know what to do when it allows repeats. I tried to do the "n choose r" method but realized it doesn't work in this case. Then I tried the permutation with order method and the results are still too small. Then I tried multiplying 10 for 10 letters to those results and it made no sense. I started thinking about the nonrepeated lettered words + "10 choose 2" times 2! + "10 choose 2" times"8 choose 2" + "10 choose 3" times"7 choose 1" + "10 choose 4" but it didn't make any sense to me.

 
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Re: Math Challenge IC Handout 6
ReynosoDavid - 2018年04月17日 Tuesday 16:28
 

Here's a hint: What can you say about the words that do not have "at least one pair of repeating letters"?

 
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