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Re: Combinations cookie problem [#permalink]
Bunuel

thanks for the explanation , my Q is why do we divide 5! by 3! and 2! (because of the repeatsi assume) can you explain that conceptually i know i am missing something fundamental here

my Q is why do we do that or how do we get to 5C2 without that line of reasoning if its there at all...

thanks
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Re: Combinations cookie problem [#permalink]
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rxs0005 wrote:
Bunuel

thanks for the explanation , my Q is why do we divide 5! by 3! and 2! (because of the repeatsi assume) can you explain that conceptually i know i am missing something fundamental here

my Q is why do we do that or how do we get to 5C2 without that line of reasoning if its there at all...

thanks


This might help: counting-ps-106762.html
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Re: A woman has seven cookies - four chocolate chip and three [#permalink]
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AM I conceptually correct when I say that 5c4 is the number of ways to choose 4 cookies out of 5 (As we have 4 children)...and then the cookies will arrange themselves among children in 4! ways
Of the cookies 3 are identical and other 2 are identical
So---> 5c4*4!/3!*2! = 10

Will this rule apply even when the cookies are 10 and the children are 4...or is it applicable coincidentally for this very specific question
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Re: A woman has seven cookies - four chocolate chip and three [#permalink]
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Bunuel wrote:
rxs0005 wrote:
A woman has seven cookies--four chocolate chip and three oatmeal. She gives one cookie to each of her six children: Nicole, Ronit, Kim, Deborah, Mark, and Terrance. If Deborah will only eat the kind of cookie that Kim eats, in how many different ways can the cookies be distributed?

(A) 5040
(B) 50
(C) 25
(D) 15
(E) 12


We have to distribute 7 cookies between 6 kids and give 7th leftover cookie for charity, so distribute 7 cookies between 7 entities: Deborah, Kim, 1, 2, 3, 4, 5.

If Deborah and Kim get chocolate cookies then there will be 2 chocolate and 3 oatmeal cookies to distribute between 5: 5!/(2!3!) = 10 (assign 5 cookies out of which 2 chocolate and 3 oatmeal cookies are identical to 5 people);

If Deborah and Kim get oatmeal cookies then there will be 4 chocolate and 1 oatmeal cookie to distribute between 5: 5!/(4!1!) = 5;

10 + 5 = 15.

Answer: D.


the approach to consider 7th left over cookie for charity is good
it helped me to cut down time for question solving
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Re: A woman has seven cookies - four chocolate chip and three [#permalink]
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Hi Bunuel

The reason you don't multiply each part by 5C2 and 3C2 to choose which 2 cookies to give Deborah and Kim is because cookies identical?

Bunuel wrote:
rxs0005 wrote:
A woman has seven cookies--four chocolate chip and three oatmeal. She gives one cookie to each of her six children: Nicole, Ronit, Kim, Deborah, Mark, and Terrance. If Deborah will only eat the kind of cookie that Kim eats, in how many different ways can the cookies be distributed?

(A) 5040
(B) 50
(C) 25
(D) 15
(E) 12


We have to distribute 7 cookies between 6 kids and give 7th leftover cookie for charity, so distribute 7 cookies between 7 entities: Deborah, Kim, 1, 2, 3, 4, 5.

If Deborah and Kim get chocolate cookies then there will be 2 chocolate and 3 oatmeal cookies to distribute between 5: 5!/(2!3!) = 10 (assign 5 cookies out of which 2 chocolate and 3 oatmeal cookies are identical to 5 people);

If Deborah and Kim get oatmeal cookies then there will be 4 chocolate and 1 oatmeal cookie to distribute between 5: 5!/(4!1!) = 5;

10 + 5 = 15.

Answer: D.
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Re: A woman has seven cookies - four chocolate chip and three [#permalink]
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can someone explain me where did i go wrong ?
my approach to this question was:
case 1 : when both D and K have oatmeal cookies -
so, we are left with 1 oatmeal cookie and 4 chocolate cookies. so we can either select all 4 chocolate cookies for the rest 4 children i.e 4c4= 1 way; or 1 oatmeal cookie and 3 chocolate cookies i.e 1c1 (for oatmeal cookies) * 4c3 (for selecting 3 out of 4 chocolate cookies) = 1* 4 = 4 ways.
so total = 1 + 4 = 5 ways

case 2: when both D and K select chocolate cookies -
so we are left with 3 oatmeal cookies and 2 chocolate cookies. so we can either select all 3 oatmeal cookies and 1 chocolate cookie for the rest 4 children i.e 3c3 * 2c1 = 1*2= 2 ways ; or select 2 oatmeal cookies and 2 chocolate cookies = 3c2 (for oatmeal) * 2c2 (for chocolate) = 3*1 = 3 ways
so total= 2+3= 5 ways

hence, overall, we have 5+5 = 10 ways
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Re: A woman has seven cookies - four chocolate chip and three [#permalink]
Bunuel wrote:
rxs0005 wrote:
A woman has seven cookies--four chocolate chip and three oatmeal. She gives one cookie to each of her six children: Nicole, Ronit, Kim, Deborah, Mark, and Terrance. If Deborah will only eat the kind of cookie that Kim eats, in how many different ways can the cookies be distributed?

(A) 5040
(B) 50
(C) 25
(D) 15
(E) 12


We have to distribute 7 cookies between 6 kids and give 7th leftover cookie for charity, so distribute 7 cookies between 7 entities: Deborah, Kim, 1, 2, 3, 4, 5.

If Deborah and Kim get chocolate cookies then there will be 2 chocolate and 3 oatmeal cookies to distribute between 5: 5!/(2!3!) = 10 (assign 5 cookies out of which 2 chocolate and 3 oatmeal cookies are identical to 5 people);

If Deborah and Kim get oatmeal cookies then there will be 4 chocolate and 1 oatmeal cookie to distribute between 5: 5!/(4!1!) = 5;

10 + 5 = 15.

Answer: D.


Hi,
In you solution above, as far as I can see, the order of distribution of cookies is considered. Could you please enlighten me why the order shall be considered here. I tried to solve the problem with the following approach but ended up with a wrong answer:

Solution
-----------------------------------------------------------------------------------------
CASE 1: Deborah + Kim both gets Chocolate cookies
Remaining chocolate cookies = 4-2 = 2
Oatmeal cookies = 3
Total cookies = 2+3 =5
Total number of ways to distribute 5 cookies among remaining 4 children = C (5,4) = 5 ways

CASE 2:Deborah + Kim both gets Oatmeal cookies
Remaining Oatmeal cookies = 3-2 = 1
Chocolate cookies = 4
Total cookies = 1+4 =5
Total number of ways to distribute 5 cookies among remaining 4 children = C (5,4) = 5 ways

Total number of ways = CASE 1 + CASE 2 = 5+5 = 10.
-------------------------------------------------------------------------------
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Re: A woman has seven cookies - four chocolate chip and three [#permalink]
Can anyone help me with this?
My reasoning:

The 2 girls get 2 chocolates,the other girls can receive either 1,2 or none chocolates.

-Number of ways to pick 2 out the remaining four, who get chocolate while the others get oatmeal: 4C2,
-Number of ways to pick 1, who gets chocolate, the other 3 get oatmeal: 4C1,
-Other 4 get all oatmeal: 1
_____________________________

The 2 girls get 2 Oatmeals:

-Number of ways to pick 1 out of 4, who gets the remaining oatmeal: 4C1;
-Other 4 get chocolate:1.
_____________________________

Total is 16.
Thanks for the help!
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Re: A woman has seven cookies - four chocolate chip and three [#permalink]
JusTLucK04 wrote:
AM I conceptually correct when I say that 5c4 is the number of ways to choose 4 cookies out of 5 (As we have 4 children)...and then the cookies will arrange themselves among children in 4! ways
Of the cookies 3 are identical and other 2 are identical
So---> 5c4*4!/3!*2! = 10

Will this rule apply even when the cookies are 10 and the children are 4...or is it applicable coincidentally for this very specific question


Bunuel
This would interest me as well! Thank you!
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A woman has seven cookies - four chocolate chip and three [#permalink]
Dear all:

I tried to do the question by subtracting the violations - Deborah and Kim eat different cookies - from the total arrangements. The total arrangements can be calculated as 7!/(4!3!)=35. In my calculation, each arrangement case for the violation produces 4 outcomes with 4 cases. The first case is Kim and Deborah eat cc and oatmeal respectively with 1 cc left over. The second case is Kim and Deborah eat cc and oatmeal with 1 oatmeal left over. The calculation for the first case assuming order is K,D,N,R,M,T is (4×3×3×2×2×1)/(3×2×1×3×2×1) =4. The denominator accounts for the duplicates. The answer I get is 35-16=19. I'd appreciate if someone can help me figure out where I am going wrong with my calculation.

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A woman has seven cookies - four chocolate chip and three [#permalink]
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olstep wrote:
JusTLucK04 wrote:
AM I conceptually correct when I say that 5c4 is the number of ways to choose 4 cookies out of 5 (As we have 4 children)...and then the cookies will arrange themselves among children in 4! ways
Of the cookies 3 are identical and other 2 are identical
So---> 5c4*4!/3!*2! = 10

Will this rule apply even when the cookies are 10 and the children are 4...or is it applicable coincidentally for this very specific question


Bunuel
This would interest me as well! Thank you!


Yes, it is correct.

5C4 * 4! = 5!
So either we pick 4 cookies out of 5 and distribute those 4 in 4! ways
or
We distribute 5 in 5! ways because there are 4 children and one Mr V (or charity).

If say there were 6 cookies and 4 children, we could pick 4 cookies out of 6 in 6C4 ways and distribute them in 4! ways. This would give us (6*5)/2 * 4! = 6!/2
or
We could distribute to 6 people in 6! ways because we have 4 children and 2 identical Mr Vs. Hence, we would divide 6! by 2 to get 6!/2

Originally posted by KarishmaB on 22 Jun 2021, 23:30.
Last edited by KarishmaB on 26 Dec 2023, 08:45, edited 1 time in total.
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Re: A woman has seven cookies - four chocolate chip and three [#permalink]
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imslogic wrote:
Dear all:

I tried to do the question by subtracting the violations - Deborah and Kim eat different cookies - from the total arrangements. The total arrangements can be calculated as 7!/(4!3!)=35. In my calculation, each arrangement case for the violation produces 4 outcomes with 4 cases. The first case is Kim and Deborah eat cc and oatmeal respectively with 1 cc left over. The second case is Kim and Deborah eat cc and oatmeal with 1 oatmeal left over. The calculation for the first case assuming order is K,D,N,R,M,T is (4×3×3×2×2×1)/(3×2×1×3×2×1) =4. The denominator accounts for the duplicates. The answer I get is 35-16=19. I'd appreciate if someone can help me figure out where I am going wrong with my calculation.

Posted from my mobile device


You're close.

Case 1: 3 Chocolate and 3 Oatmeal
K has 6 options.
No matter what K chooses, D has 3 options.
The third to choose has 4 options.
The fourth to choose has 3 options.
The fifth to choose has 2 options.
The sixth to choose has 1 option.

6*3*4*3*2*1 / 3*2*1*3*2*1 = 3*4 = 12

Case 2A: 4 Chocolate and 2 Oatmeal; K chooses Chocolate and D chooses Oatmeal
K has 4 options.
D has 2 options.
The third to choose has 4 options.
The fourth to choose has 3 options.
The fifth to choose has 2 options.
The sixth to choose has 1 option.

4*2*4*3*2*1 / 4*3*2*1*2*1 = 4

Case 2B: 4 Chocolate and 2 Oatmeal; K chooses Oatmeal and D chooses Chocolate
K has 2 options.
D has 4 options.
The third to choose has 4 options.
The fourth to choose has 3 options.
The fifth to choose has 2 options.
The sixth to choose has 1 option.

Same as 2A = 4

Total disallowed options is 12+4+4 = 20.

30-20 = 15

Answer choice D.
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Re: A woman has seven cookies - four chocolate chip and three [#permalink]
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fe21 wrote:
Can anyone help me with this?
My reasoning:

The 2 girls get 2 chocolates,the other girls can receive either 1,2 or none chocolates.

-Number of ways to pick 2 out the remaining four, who get chocolate while the others get oatmeal: 4C2,
-Number of ways to pick 1, who gets chocolate, the other 3 get oatmeal: 4C1,
-Other 4 get all oatmeal: 1
_____________________________

The 2 girls get 2 Oatmeals:

-Number of ways to pick 1 out of 4, who gets the remaining oatmeal: 4C1;
-Other 4 get chocolate:1.
_____________________________

Total is 16.
Thanks for the help!


Other 4 all get oatmeal? With only 3 oatmeals? Gonna be a fight!!
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Re: A woman has seven cookies - four chocolate chip and three [#permalink]
Is it possible to solve this using the division & distribution method?

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Re: A woman has seven cookies - four chocolate chip and three [#permalink]
Please tell why my reasoning is wrong?We have 4 Chocolate & 3 Oatmeal cookie
Case: 1 (Kim and Deborah eats oatmeal cookie)
We're left with- 4Choc& 1 Oatmeal cookie
Now,
>>All 4 chocolate cookies are distributed: 4C4 = 1 way
>> 3 Choc and 1 oatmeal is given: 4C3*1C1*(4!/3!)=16 ways

Case: 2 (Kim and Deborah eats Chocolate cookie)
We're left with- 2Choc& 3Oatmeal cookie
>>3 Oatmeal and 1 chocolate cookie: 3C3*2C1*(4!/3!)=8ways
>>2 Oatmeal and 2 chocolate cookie: 2C2*3C2*(4!/2! 2!)= 18 ways

Total= 43

Where am i going wrong in my though process??
chetan2u Bunuel bb KarishmaB
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Re: A woman has seven cookies - four chocolate chip and three [#permalink]
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Sans8 wrote:
Please tell why my reasoning is wrong?We have 4 Chocolate & 3 Oatmeal cookie
Case: 1 (Kim and Deborah eats oatmeal cookie)
We're left with- 4Choc& 1 Oatmeal cookie
Now,
>>All 4 chocolate cookies are distributed: 4C4 = 1 way
>> 3 Choc and 1 oatmeal is given: 4C3*1C1*(4!/3!)=16 ways

Case: 2 (Kim and Deborah eats Chocolate cookie)
We're left with- 2Choc& 3Oatmeal cookie
>>3 Oatmeal and 1 chocolate cookie: 3C3*2C1*(4!/3!)=8ways
>>2 Oatmeal and 2 chocolate cookie: 2C2*3C2*(4!/2! 2!)= 18 ways

Total= 43

Where am i going wrong in my though process??
chetan2u Bunuel bb KarishmaB


You are arranging these cookies which is wrong and also the calculations are wrong.
See the red portion.

Case: 1 (Kim and Deborah eats oatmeal cookie)
We're left with- 4Choc& 1 Oatmeal cookie
Now,
>>All 4 chocolate cookies are distributed: 4C4 = 1 way
>> Choose 3 friends and give them chocolate, fourth will automatically get oatmeal3 Choc and 1 oatmeal is given: 4C3*1C1*(4!/3!)=16=4 ways

Case: 2 (Kim and Deborah eats Chocolate cookie)
We're left with- 2Choc& 3Oatmeal cookie
>> Choose 3 friends and give them oatmeal, fourth will automatically get choc => 4C3*1C1=4
3 Oatmeal and 1 chocolate cookie: 4C3*2C1*(4!/3!)=8=2 ways

>> Choose 2 friends and give them chocolate, other two will automatically get oatmeal => 4C2*2C2=6
2 Oatmeal and 2 chocolate cookie: 2C2*3C2*(4!/2! 2!)= 18 ways=6 ways


Total= 43 1+4+4+6=15
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Re: A woman has seven cookies - four chocolate chip and three [#permalink]
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Sans8 wrote:
Please tell why my reasoning is wrong?We have 4 Chocolate & 3 Oatmeal cookie
Case: 1 (Kim and Deborah eats oatmeal cookie)
We're left with- 4Choc& 1 Oatmeal cookie
Now,
>>All 4 chocolate cookies are distributed: 4C4 = 1 way
>> 3 Choc and 1 oatmeal is given: 4C3*1C1*(4!/3!)=16 ways

Case: 2 (Kim and Deborah eats Chocolate cookie)
We're left with- 2Choc& 3Oatmeal cookie
>>3 Oatmeal and 1 chocolate cookie: 3C3*2C1*(4!/3!)=8ways
>>2 Oatmeal and 2 chocolate cookie: 2C2*3C2*(4!/2! 2!)= 18 ways


Total= 43

Where am i going wrong in my though process??
chetan2u Bunuel bb KarishmaB


The highlighted are incorrect.

>> 3 Choc and 1 oatmeal is given: 4C3*1C1*(4!/3!)=16 ways
You cannot use 4C3 to select 3 chocolate cookies out of 4. Note that all chocolate cookies are the same. So we have only 1 way of selecting 3 chocolate cookies out of 4 - pick any 3.


>>3 Oatmeal and 1 chocolate cookie: 3C3*2C1*(4!/3!)=8ways
>>2 Oatmeal and 2 chocolate cookie: 2C2*3C2*(4!/2! 2!)= 18 ways


Similarly, here you cannot use 2C1 to select 1 chocolate cookie out of 2 because both are same. Again, you cannot use 3C2 because all chocolate cookies are the same. Solve without these figures and you will get your answer.
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Re: A woman has seven cookies - four chocolate chip and three [#permalink]
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