# permutations

• Feb 11th 2009, 03:33 PM
william
permutations
1.a)Find the number of 4*4 patterns you can make using eight white,four grey,four blue tiles,

my thinking $\displaystyle \frac{16}{8!4!4!}=900,900$

b) How many different 10-digit telephone numbers contain four 2s three 3s and three 7s?

c) A band has recorded five hit singles. In how many different orders could the band play three of these five songs at a concert?
• Feb 11th 2009, 05:29 PM
Plato
Look at the graphs. They are all the same colorings.
Do you see why?
• Feb 11th 2009, 05:42 PM
Jhevon
Quote:

Originally Posted by william
b) How many different 10-digit telephone numbers contain four 2s three 3s and three 7s?

hint: find the number of ways to permute the 10 "objects" (the numbers here are the objects) and divide out the repeats (if you, for instance, switch one 2 with another, you get the same phone number, you must get rid of repeats so that you don't count the cases where you switch numbers with themselves).

Quote:

c) A band has recorded five hit singles. In how many different orders could the band play three of these five songs at a concert?
hint: you have 5 choices for the first song, 4 for the second, and 3 for the third.