Martin's Dance Playlist

Martin's iPod has 24 24 songs on it. He wants to make a playlist consisting of three songs to dance to. Let N N be the number of different playlists Martin can make. What are the last 3 3 digits of N N ?

Details and assumptions

The order of the songs matter.

The songs in the playlist should be distinct from each other.


The answer is 144.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

9 solutions

Josh Petrin
Aug 8, 2013

We can count systematically, since whatever we choose to be the first song in the playlist cannot be chosen as the second, and whatever we choose for the first and second song cannot be chosen for the third. Thus, by the product rule, the number of possible ordered playlists is 24 × ( 24 1 ) × ( 24 2 ) = 12144 , 24 \times (24 - 1) \times (24 - 2) = 12144, and the last three digits of this is 144 \boxed{144} .

Barometer Nongbri
Aug 10, 2013

permutation of 24 things taking 3 at a time. 24P3=22 23 24=12144

Sablis Salam
Aug 9, 2013

N = 24P3 = 12144 , so the last 3 digits of N = 144

Mike Andrew Baes
Aug 7, 2013

There are 24 songs and the playlist could only have 3 songs (with orders matter). We may use permutation in this problem: 24P3=12144 Therefore, the answer to the question is 144.

Zx Yeoh
Aug 7, 2013

The number of playlists which can be formed is: 24 × 23 × 22 24 \times 23 \times 22 . Since only the last 3 digits are needed, just multiply 24 × 3 × 2 24 \times 3 \times 2 and you'll get 144. ( 4 × 3 × 2 4 \times 3 \times 2 doesn't give you a 3-digit answer)

A A
Aug 5, 2013

We can choose 3 3 songs from 24 24 songs in 24 P 3 = 12144 ^{24}P_3 = 12144

Now , 12144 144 ( m o d 100 ) 12144 \equiv \boxed {144} \pmod{100}

There is a mistake on the last line. That will be 12144 144 ( m o d 1000 ) 12144 \equiv \boxed {144} \pmod{1000}

A A - 7 years, 10 months ago
Akira Sonoda
Aug 5, 2013

Permuation is the key word.

So, P ( 24 , 3 ) P ( 24 , 3 )

24 × 23 × 22 24 \times 23 \times 22

They equal 12144. Answer is 144 144

12144 ≡ 144 ( mod 1000)

Sablis Salam - 7 years, 10 months ago
Ahmed Lo'ay
Aug 5, 2013

24P3=12144

the last three digits are 144 :)

24P3 = 24 * 23 * 22

Ahmed Lo'ay - 7 years, 10 months ago

According to the given situation, total number of songs are 24.

Martin wants to make a playlist of 3 songs where order of songs matter.

This is similar to the case when we want to select and arrange 3 objects out of 24.

24 ! ( 24 3 ) ! \frac{24!}{(24-3)!} = 24 ! 22 ! \frac{24!}{22!} = 12144 \mathrm{12144}

Hence our final answer is 144 \fbox{144}

Actually, 24 ! ( 24 3 ) ! = 24 ! 21 ! \frac{24!}{(24-3)!} = \frac{24!}{21!} , not 24 ! 22 ! \frac{24!}{22!} , although you did get the right answer. :/

Josh Petrin - 7 years, 10 months ago

Log in to reply

Oops,Sorry!

Manish Kumar Mishra - 7 years, 10 months ago

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...