in how many ways can 12 books be divided among 3 boys so that each receives 4 books?
A 36540
B 34560
C 34650
D 35640
E 36450
Permutations/Combinations
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Take the task of distributing the 12 books and break it into stagesvaibhav101 wrote:in how many ways can 12 books be divided among 3 boys so that each receives 4 books?
A 36540
B 34560
C 34650
D 35640
E 36450
Let's say the children are named A, B and C
Stage 1: Select 4 books to give to child A
Since the order in which we select the 4 books does not matter, we can use combinations.
We can select 4 books from 12 books in 12C4 ways (= 12!/(4!)(8!))
So, we can complete stage 1 in 12!/(4!)(8!) ways
Stage 2: select 4 books to give to child B
There are now 8 books remaining
We can select 4 books from 8 books in 8C4 ways (= 8!/(4!)(4!))
So, we can complete stage 2 in 8!/(4!)(4!) ways
Stage 4: select 4 books to give to child C
There are now 4 books remaining
NOTE: There's only 1 way to select 4 books from 4 books, but if we want this result to look like the others, let's do the following:
We can select 4 books from 4 books in 4C4 ways (= 4!/4!)
So, we can complete stage 3 in 4!/4! ways
By the Fundamental Counting Principle (FCP), we can complete all 3 stages (and thus distribute all 12 books) in [12!/(4!)(8!)][8!/(4!)(4!)][4!/4!] ways
A BUNCH of terms cancel out to give us 12!/(4!)³, which evaluates to be 34650
Answer: C
--------------------------
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Once a boy receives 4 books, the order in which he receives them doesn't matter. So the first boy has 12C4 ways to receive his 4 books, the second boy has 8C4 ways to receive his 4 books and the third boy has 4C4 ways to receive his books. So the total number of ways the 3 boys can receive 4 books each isvaibhav101 wrote:in how many ways can 12 books be divided among 3 boys so that each receives 4 books?
A 36540
B 34560
C 34650
D 35640
E 36450
12C4 x 8C4 x 4C4
(12 x 11 x 10 x 9)/(4 x 3 x 2) x (8 x 7 x 6 x 5)/(4 x 3 x 2) x 1
11 x 5 x 9 x 2 x 7 x 5
34650
Answer: C
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