Question 34935: Anothe one that is confusing to me. Thank you for your help! THIS IS A HARD ONE!
Solve any way and show work.
How many 3-digit numbers are possible using 2,3,5, or 7 if you DO NOT repeat digits?
Answer by longjonsilver(2297)   (Show Source):
You can put this solution on YOUR website! OK long way first:
235 325 523 723
237 327 527 725
253 352 532 732
257 357 537 735
273 372 572 752
275 375 573 753
there are no other 3 digit numbers made up from 2,3,5 or 7.
So... "quick" method:
Think of the number like ABC... how many numbers could be placed in position A? Answer any of the 4.
OK, so we have a number in position A. Whatever it is, we now have 3 numbers left to put into position B, so altogether we have 4*3 possibilities.
And finally we have 2 numbers to put into position C, so altogether we have 4*3*2 permutations --> 24.
Count the number of examples i wrote at the start: there are 24 different 3 digit numbers.
jon
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