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Re: A bakery currently has 5 pies and 6 cakes in its inventory [#permalink]
Thanks Bunuel for the concise explanation!
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Re: A bakery currently has 5 pies and 6 cakes in its inventory [#permalink]
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JubtaGubar wrote:
A bakery currently has 5 pies and 6 cakes in its inventory. The bakery’s owner has decided to display 5 of these items in the bakery’s front window. If the items are randomly selected, what is the probability that the display will have exactly 3 pies?

A 3/11
B. 25/77
C. 5/11
D. 7/11
E. 50/77


Pie (pie) pie (cake) (cake) = (5/11) (4/10) (3/9) (6/8) (5/7) 5!/(3!.2!) = 25/77
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Re: A bakery currently has 5 pies and 6 cakes in its inventory [#permalink]
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JubtaGubar wrote:
A bakery currently has 5 pies and 6 cakes in its inventory. The bakery’s owner has decided to display 5 of these items in the bakery’s front window. If the items are randomly selected, what is the probability that the display will have exactly 3 pies?

A 3/11
B. 25/77
C. 5/11
D. 7/11
E. 50/77


Answer: option b

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Re: A bakery currently has 5 pies and 6 cakes in its inventory [#permalink]
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Bunuel wrote:
JubtaGubar wrote:
A bakery currently has 5 pies and 6 cakes in its inventory. The bakery’s owner has decided to display 5 of these items in the bakery’s front window. If the items are randomly selected, what is the probability that the display will have exactly 3 pies?

A 3/11
B. 25/77
C. 5/11
D. 7/11
E. 50/77


Combination approach:

\(\frac{C^3_5*C^2_6}{C^5_{11}}=\frac{25}{77}\), where:
\(C^3_5\) is # of ways to chose 3 pies out of 5;
\(C^2_5\) is # of ways to chose 2 cakes out of 6;
\(C^5_{11}\) is # of ways to chose 5 items out of total 5+6=11.


Answer: B.

Probability approach:

We need the probability that the owner will select PPPCC: \(\frac{5!}{3!*2!}*(\frac{5}{11}*\frac{4}{10}*\frac{3}{9})*(\frac{6}{8}*\frac{5}{7})=\frac{25}{77}\), we are multiplying by \(\frac{5!}{3!*2!}\) since PPPCC scenario can occur in number of ways: PPPCC, PPCPC, PCPPC, CPPPC, ... Notice that the number of occurrences of PPPCC basically is the number of arrangements of 5 letters PPPCC out of which 3 P's and 2 C's are identical, so it's \(\frac{5!}{3!*2!}\) .

Answer: B.

Hope it's clear.



[b]\(C^2_5\) is # of ways to chose 2 cakes out of 6;(this should be C^2_6)?
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Re: A bakery currently has 5 pies and 6 cakes in its inventory [#permalink]
Expert Reply
Williamhomey12 wrote:
Bunuel wrote:
JubtaGubar wrote:
A bakery currently has 5 pies and 6 cakes in its inventory. The bakery’s owner has decided to display 5 of these items in the bakery’s front window. If the items are randomly selected, what is the probability that the display will have exactly 3 pies?

A 3/11
B. 25/77
C. 5/11
D. 7/11
E. 50/77


Combination approach:

\(\frac{C^3_5*C^2_6}{C^5_{11}}=\frac{25}{77}\), where:
\(C^3_5\) is # of ways to chose 3 pies out of 5;
\(C^2_5\) is # of ways to chose 2 cakes out of 6;
\(C^5_{11}\) is # of ways to chose 5 items out of total 5+6=11.


Answer: B.

Probability approach:

We need the probability that the owner will select PPPCC: \(\frac{5!}{3!*2!}*(\frac{5}{11}*\frac{4}{10}*\frac{3}{9})*(\frac{6}{8}*\frac{5}{7})=\frac{25}{77}\), we are multiplying by \(\frac{5!}{3!*2!}\) since PPPCC scenario can occur in number of ways: PPPCC, PPCPC, PCPPC, CPPPC, ... Notice that the number of occurrences of PPPCC basically is the number of arrangements of 5 letters PPPCC out of which 3 P's and 2 C's are identical, so it's \(\frac{5!}{3!*2!}\) .

Answer: B.

Hope it's clear.



[b]\(C^2_5\) is # of ways to chose 2 cakes out of 6;(this should be C^2_6)?

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Edited the typo. Thank you.
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Re: A bakery currently has 5 pies and 6 cakes in its inventory [#permalink]
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JubtaGubar wrote:
A bakery currently has 5 pies and 6 cakes in its inventory. The bakery’s owner has decided to display 5 of these items in the bakery’s front window. If the items are randomly selected, what is the probability that the display will have exactly 3 pies?

A 3/11
B. 25/77
C. 5/11
D. 7/11
E. 50/77


total items; 11
so arragement of 5 items at display can be done in 11c5 ways ;
and exactly 3 pies and 2 cakes; 5c3*6c2
so P = 5c3*6c2/ 11c5 = 25/77
IMO B :cool:
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A bakery currently has 5 pies and 6 cakes in its inventory [#permalink]
Expert Reply

Solution


Given:
    • A bakery currently has 5 pies and 6 cakes in its inventory
    • The bakery’s owner has decided to display 5 of these items in the bakery’s front window

To find:
    • The probability that the display will have exactly 3 pies

Approach and Working Out:
    • Sample size = \(^{11}C_5\)
    • Number of ways of selecting 5 items such that the display will have exactly 3 pies = \(^5C_3 * ^6C_2\)• Therefore, the probability = \(\frac{^5C_3 * ^6C_2}{^{11}C_5} = \frac{25}{77}\)

Hence, the correct answer is Option B.

Answer: B

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A bakery currently has 5 pies and 6 cakes in its inventory [#permalink]
Quote:
A bakery currently has 5 pies and 6 cakes in its inventory. The bakery’s owner has decided to display 5 of these items in the bakery’s front window. If the items are randomly selected, what is the probability that the display will have exactly 3 pies?


Total outcomes = 11!/(5!*6!) -> 462
Desired outcomes = 5!/(3!*2!) * 6!/(2!*4!) -> 150

Probability = 150/462 -> 25/77

Answer -> B
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Re: A bakery currently has 5 pies and 6 cakes in its inventory [#permalink]
JubtaGubar wrote:
My calculation is the following:
5/11 * 4/10 * 3/9 * 6/8 * 5/7 = 5/77
but there is no such solution.
could you please explain why is this method incorrect?




That is because you have only considered the situation where three pies are selected first and then two cakes are selected, i.e PPPCC.
However. you need to take into account other scenarios also, such as PCCPP, CCPPP etc.
Therefore solution will be \(\frac{5}{77}\) * \(\frac{5!}{3!*2!}\)
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Re: A bakery currently has 5 pies and 6 cakes in its inventory [#permalink]
you can just do 1 / (3/5/11x6).
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Re: A bakery currently has 5 pies and 6 cakes in its inventory [#permalink]
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