**Re: I really can't do these!**
autumnfilby said:

24. Find the number of combinations of letters taken four at a time that can formed from the set of letters M A T H E M A T I C S.

I've tried it like 75483923948738 times, and I don't understand. An explanation in addition to an answer is WONDEROUS! If I figure out how to do one, I can probably do the rest.

Thanks so much, Autumn

Your question might have more than one interpretation. Here is one analysis.

The word mathematics contains the letters m, a, t, h, e, i, c and s for a total of seven letters. We have a string of four letters designated by four empty spaces....

__ __ __ __

Now, how many letters can be placed in the first space? 7?

How many letters can placed in the second space? 7?

etc.

The number of combinations would be 7*7*7*7 or 7[sup:1ifoaqr2]4[/sup:1ifoaqr2].

Bear in mind that other interpretations of the question might include that no letter can be used more times than it appears in the word "mathematics" or no letter can be used more than once. Those pose different problems. Maybe you should post your questions using the exact wording of the problem as presented to you.